Errors | Node.js v9.6.0 Documentation

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# Errors#

Applications running in Node.js will generally experience four categories of errors:

- Standard JavaScript errors such as:
  - <EvalError> : thrown when a call to `eval()` fails.
  - <SyntaxError> : thrown in response to improper JavaScript language syntax.
  - <RangeError> : thrown when a value is not within an expected range
  - <ReferenceError> : thrown when using undefined variables
  - <TypeError> : thrown when passing arguments of the wrong type
  - <URIError> : thrown when a global URI handling function is misused.
- System errors triggered by underlying operating system constraints such as attempting to open a file that does not exist, attempting to send data over a closed socket, etc;
- And User-specified errors triggered by application code.
- Assertion Errors are a special class of error that can be triggered whenever Node.js detects an exceptional logic violation that should never occur. These are raised typically by the `assert` module.

All JavaScript and System errors raised by Node.js inherit from, or are instances of, the standard JavaScript <Error> class and are guaranteed to provide at least the properties available on that class.

## Error Propagation and Interception#

Node.js supports several mechanisms for propagating and handling errors that occur while an application is running. How these errors are reported and handled depends entirely on the type of Error and the style of the API that is called.

All JavaScript errors are handled as exceptions that immediately generate and throw an error using the standard JavaScript `throw` mechanism. These are handled using the `try / catch` construct provided by the JavaScript language.

    // Throws with a ReferenceError because z is undefined
    try {
      const m = 1;
      const n = m + z;
    } catch (err) {
      // Handle the error here.
    }

Any use of the JavaScript `throw` mechanism will raise an exception that must be handled using `try / catch` or the Node.js process will exit immediately.

With few exceptions, Synchronous APIs (any blocking method that does not accept a `callback` function, such as `fs.readFileSync`), will use `throw` to report errors.

Errors that occur within Asynchronous APIs may be reported in multiple ways:

- Most asynchronous methods that accept a `callback` function will accept an `Error` object passed as the first argument to that function. If that first argument is not `null` and is an instance of `Error`, then an error occurred that should be handled.

      const fs = require('fs');
      fs.readFile('a file that does not exist', (err, data) => {
        if (err) {
          console.error('There was an error reading the file!', err);
          return;
        }
        // Otherwise handle the data
      });

- When an asynchronous method is called on an object that is an `EventEmitter`, errors can be routed to that object's `'error'` event.

      const net = require('net');
      const connection = net.connect('localhost');

      // Adding an 'error' event handler to a stream:
      connection.on('error', (err) => {
        // If the connection is reset by the server, or if it can't
        // connect at all, or on any sort of error encountered by
        // the connection, the error will be sent here.
        console.error(err);
      });

      connection.pipe(process.stdout);

- A handful of typically asynchronous methods in the Node.js API may still use the `throw` mechanism to raise exceptions that must be handled using `try / catch`. There is no comprehensive list of such methods; please refer to the documentation of each method to determine the appropriate error handling mechanism required.

The use of the `'error'` event mechanism is most common for stream-based and event emitter-based APIs, which themselves represent a series of asynchronous operations over time (as opposed to a single operation that may pass or fail).

For all `EventEmitter` objects, if an `'error'` event handler is not provided, the error will be thrown, causing the Node.js process to report an unhandled exception and crash unless either: The `domain` module is used appropriately or a handler has been registered for the `process.on('uncaughtException')` event.

    const EventEmitter = require('events');
    const ee = new EventEmitter();

    setImmediate(() => {
      // This will crash the process because no 'error' event
      // handler has been added.
      ee.emit('error', new Error('This will crash'));
    });

Errors generated in this way cannot be intercepted using `try / catch` as they are thrown after the calling code has already exited.

Developers must refer to the documentation for each method to determine exactly how errors raised by those methods are propagated.

### Error-first callbacks#

Most asynchronous methods exposed by the Node.js core API follow an idiomatic pattern referred to as an error-first callback (sometimes referred to as a Node.js style callback). With this pattern, a callback function is passed to the method as an argument. When the operation either completes or an error is raised, the callback function is called with the Error object (if any) passed as the first argument. If no error was raised, the first argument will be passed as `null`.

    const fs = require('fs');

    function errorFirstCallback(err, data) {
      if (err) {
        console.error('There was an error', err);
        return;
      }
      console.log(data);
    }

    fs.readFile('/some/file/that/does-not-exist', errorFirstCallback);
    fs.readFile('/some/file/that/does-exist', errorFirstCallback);

The JavaScript `try / catch` mechanism cannot be used to intercept errors generated by asynchronous APIs. A common mistake for beginners is to try to use `throw` inside an error-first callback:

    // THIS WILL NOT WORK:
    const fs = require('fs');

    try {
      fs.readFile('/some/file/that/does-not-exist', (err, data) => {
        // mistaken assumption: throwing here...
        if (err) {
          throw err;
        }
      });
    } catch (err) {
      // This will not catch the throw!
      console.error(err);
    }

This will not work because the callback function passed to `fs.readFile()` is called asynchronously. By the time the callback has been called, the surrounding code (including the `try { } catch (err) { }` block will have already exited. Throwing an error inside the callback can crash the Node.js process in most cases. If domains are enabled, or a handler has been registered with `process.on('uncaughtException')`, such errors can be intercepted.

## Class: Error#

A generic JavaScript `Error` object that does not denote any specific circumstance of why the error occurred. `Error` objects capture a "stack trace" detailing the point in the code at which the `Error` was instantiated, and may provide a text description of the error.

For crypto only, `Error` objects will include the OpenSSL error stack in a separate property called `opensslErrorStack` if it is available when the error is thrown.

All errors generated by Node.js, including all System and JavaScript errors, will either be instances of, or inherit from, the `Error` class.

### new Error(message)#

- `message` <string>

Creates a new `Error` object and sets the `error.message` property to the provided text message. If an object is passed as `message`, the text message is generated by calling `message.toString()`. The `error.stack` property will represent the point in the code at which `new Error()` was called. Stack traces are dependent on V8's stack trace API. Stack traces extend only to either (a) the beginning of synchronous code execution, or (b) the number of frames given by the property `Error.stackTraceLimit`, whichever is smaller.

### Error.captureStackTrace(targetObject[, constructorOpt])#

- `targetObject` <Object>
- `constructorOpt` <Function>

Creates a `.stack` property on `targetObject`, which when accessed returns a string representing the location in the code at which `Error.captureStackTrace()` was called.

    const myObject = {};
    Error.captureStackTrace(myObject);
    myObject.stack;  // similar to `new Error().stack`

The first line of the trace will be prefixed with `${myObject.name}: ${myObject.message}`.

The optional `constructorOpt` argument accepts a function. If given, all frames above `constructorOpt`, including `constructorOpt`, will be omitted from the generated stack trace.

The `constructorOpt` argument is useful for hiding implementation details of error generation from an end user. For instance:

    function MyError() {
      Error.captureStackTrace(this, MyError);
    }

    // Without passing MyError to captureStackTrace, the MyError
    // frame would show up in the .stack property. By passing
    // the constructor, we omit that frame, and retain all frames below it.
    new MyError().stack;

### Error.stackTraceLimit#

- <number>

The `Error.stackTraceLimit` property specifies the number of stack frames collected by a stack trace (whether generated by `new Error().stack` or `Error.captureStackTrace(obj)`).

The default value is `10` but may be set to any valid JavaScript number. Changes will affect any stack trace captured after the value has been changed.

If set to a non-number value, or set to a negative number, stack traces will not capture any frames.

### error.code#

- <string>

The `error.code` property is a string label that identifies the kind of error. See Node.js Error Codes for details about specific codes.

### error.message#

- <string>

The `error.message` property is the string description of the error as set by calling `new Error(message)`. The `message` passed to the constructor will also appear in the first line of the stack trace of the `Error`, however changing this property after the `Error` object is created may not change the first line of the stack trace (for example, when `error.stack` is read before this property is changed).

    const err = new Error('The message');
    console.error(err.message);
    // Prints: The message

### error.stack#

- <string>

The `error.stack` property is a string describing the point in the code at which the `Error` was instantiated.

For example:

    Error: Things keep happening!
       at /home/gbusey/file.js:525:2
       at Frobnicator.refrobulate (/home/gbusey/business-logic.js:424:21)
       at Actor.<anonymous> (/home/gbusey/actors.js:400:8)
       at increaseSynergy (/home/gbusey/actors.js:701:6)

The first line is formatted as `<error class name>: <error message>`, and is followed by a series of stack frames (each line beginning with "at "). Each frame describes a call site within the code that lead to the error being generated. V8 attempts to display a name for each function (by variable name, function name, or object method name), but occasionally it will not be able to find a suitable name. If V8 cannot determine a name for the function, only location information will be displayed for that frame. Otherwise, the determined function name will be displayed with location information appended in parentheses.

Frames are only generated for JavaScript functions. If, for example, execution synchronously passes through a C++ addon function called `cheetahify` which itself calls a JavaScript function, the frame representing the `cheetahify` call will not be present in the stack traces:

    const cheetahify = require('./native-binding.node');

    function makeFaster() {
      // cheetahify *synchronously* calls speedy.
      cheetahify(function speedy() {
        throw new Error('oh no!');
      });
    }

    makeFaster();
    // will throw:
    //   /home/gbusey/file.js:6
    //       throw new Error('oh no!');
    //           ^
    //   Error: oh no!
    //       at speedy (/home/gbusey/file.js:6:11)
    //       at makeFaster (/home/gbusey/file.js:5:3)
    //       at Object.<anonymous> (/home/gbusey/file.js:10:1)
    //       at Module._compile (module.js:456:26)
    //       at Object.Module._extensions..js (module.js:474:10)
    //       at Module.load (module.js:356:32)
    //       at Function.Module._load (module.js:312:12)
    //       at Function.Module.runMain (module.js:497:10)
    //       at startup (node.js:119:16)
    //       at node.js:906:3

The location information will be one of:

- `native`, if the frame represents a call internal to V8 (as in `[].forEach`).
- `plain-filename.js:line:column`, if the frame represents a call internal to Node.js.
- `/absolute/path/to/file.js:line:column`, if the frame represents a call in a user program, or its dependencies.

The string representing the stack trace is lazily generated when the `error.stack` property is accessed.

The number of frames captured by the stack trace is bounded by the smaller of `Error.stackTraceLimit` or the number of available frames on the current event loop tick.

System-level errors are generated as augmented `Error` instances, which are detailed here.

## Class: AssertionError#

A subclass of `Error` that indicates the failure of an assertion. Such errors commonly indicate inequality of actual and expected value.

For example:

    assert.strictEqual(1, 2);
    // AssertionError [ERR_ASSERTION]: 1 === 2

## Class: RangeError#

A subclass of `Error` that indicates that a provided argument was not within the set or range of acceptable values for a function; whether that is a numeric range, or outside the set of options for a given function parameter.

For example:

    require('net').connect(-1);
    // throws "RangeError: "port" option should be >= 0 and < 65536: -1"

Node.js will generate and throw `RangeError` instances immediately as a form of argument validation.

## Class: ReferenceError#

A subclass of `Error` that indicates that an attempt is being made to access a variable that is not defined. Such errors commonly indicate typos in code, or an otherwise broken program.

While client code may generate and propagate these errors, in practice, only V8 will do so.

    doesNotExist;
    // throws ReferenceError, doesNotExist is not a variable in this program.

Unless an application is dynamically generating and running code, `ReferenceError` instances should always be considered a bug in the code or its dependencies.

## Class: SyntaxError#

A subclass of `Error` that indicates that a program is not valid JavaScript. These errors may only be generated and propagated as a result of code evaluation. Code evaluation may happen as a result of `eval`, `Function`, `require`, or vm. These errors are almost always indicative of a broken program.

    try {
      require('vm').runInThisContext('binary ! isNotOk');
    } catch (err) {
      // err will be a SyntaxError
    }

`SyntaxError` instances are unrecoverable in the context that created them – they may only be caught by other contexts.

## Class: TypeError#

A subclass of `Error` that indicates that a provided argument is not an allowable type. For example, passing a function to a parameter which expects a string would be considered a TypeError.

    require('url').parse(() => { });
    // throws TypeError, since it expected a string

Node.js will generate and throw `TypeError` instances immediately as a form of argument validation.

## Exceptions vs. Errors#

A JavaScript exception is a value that is thrown as a result of an invalid operation or as the target of a `throw` statement. While it is not required that these values are instances of `Error` or classes which inherit from `Error`, all exceptions thrown by Node.js or the JavaScript runtime will be instances of Error.

Some exceptions are unrecoverable at the JavaScript layer. Such exceptions will always cause the Node.js process to crash. Examples include `assert()` checks or `abort()` calls in the C++ layer.

## System Errors#

System errors are generated when exceptions occur within the program's runtime environment. Typically, these are operational errors that occur when an application violates an operating system constraint such as attempting to read a file that does not exist or when the user does not have sufficient permissions.

System errors are typically generated at the syscall level: an exhaustive list of error codes and their meanings is available by running `man 2 intro` or `man 3 errno` on most Unices; or online.

In Node.js, system errors are represented as augmented `Error` objects with added properties.

### Class: System Error#

#### error.code#

- <string>

The `error.code` property is a string representing the error code, which is typically `E` followed by a sequence of capital letters.

#### error.errno#

- <string> | <number>

The `error.errno` property is a number or a string. The number is a negative value which corresponds to the error code defined in `libuv Error handling`. See uv-errno.h header file (`deps/uv/include/uv-errno.h` in the Node.js source tree) for details. In case of a string, it is the same as `error.code`.

#### error.syscall#

- <string>

The `error.syscall` property is a string describing the syscall that failed.

#### error.path#

- <string>

When present (e.g. in `fs` or `child_process`), the `error.path` property is a string containing a relevant invalid pathname.

#### error.address#

- <string>

When present (e.g. in `net` or `dgram`), the `error.address` property is a string describing the address to which the connection failed.

#### error.port#

- <number>

When present (e.g. in `net` or `dgram`), the `error.port` property is a number representing the connection's port that is not available.

### Common System Errors#

This list is not exhaustive, but enumerates many of the common system errors encountered when writing a Node.js program. An exhaustive list may be found here.

- `EACCES` (Permission denied): An attempt was made to access a file in a way forbidden by its file access permissions.

- `EADDRINUSE` (Address already in use): An attempt to bind a server (`net`, `http`, or `https`) to a local address failed due to another server on the local system already occupying that address.

- `ECONNREFUSED` (Connection refused): No connection could be made because the target machine actively refused it. This usually results from trying to connect to a service that is inactive on the foreign host.

- `ECONNRESET` (Connection reset by peer): A connection was forcibly closed by a peer. This normally results from a loss of the connection on the remote socket due to a timeout or reboot. Commonly encountered via the `http` and `net` modules.

- `EEXIST` (File exists): An existing file was the target of an operation that required that the target not exist.

- `EISDIR` (Is a directory): An operation expected a file, but the given pathname was a directory.

- `EMFILE` (Too many open files in system): Maximum number of file descriptors allowable on the system has been reached, and requests for another descriptor cannot be fulfilled until at least one has been closed. This is encountered when opening many files at once in parallel, especially on systems (in particular, macOS) where there is a low file descriptor limit for processes. To remedy a low limit, run `ulimit -n 2048` in the same shell that will run the Node.js process.

- `ENOENT` (No such file or directory): Commonly raised by `fs` operations to indicate that a component of the specified pathname does not exist -- no entity (file or directory) could be found by the given path.

- `ENOTDIR` (Not a directory): A component of the given pathname existed, but was not a directory as expected. Commonly raised by `fs.readdir`.

- `ENOTEMPTY` (Directory not empty): A directory with entries was the target of an operation that requires an empty directory -- usually `fs.unlink`.

- `EPERM` (Operation not permitted): An attempt was made to perform an operation that requires elevated privileges.

- `EPIPE` (Broken pipe): A write on a pipe, socket, or FIFO for which there is no process to read the data. Commonly encountered at the `net` and `http` layers, indicative that the remote side of the stream being written to has been closed.

- `ETIMEDOUT` (Operation timed out): A connect or send request failed because the connected party did not properly respond after a period of time. Usually encountered by `http` or `net` -- often a sign that a `socket.end()` was not properly called.

## Node.js Error Codes#

### ERR_ARG_NOT_ITERABLE##

An iterable argument (i.e. a value that works with `for...of` loops) was required, but not provided to a Node.js API.

### ERR_ASSERTION##

A special type of error that can be triggered whenever Node.js detects an exceptional logic violation that should never occur. These are raised typically by the `assert` module.

### ERR_ASYNC_CALLBACK##

An attempt was made to register something that is not a function as an `AsyncHooks` callback.

### ERR_ASYNC_TYPE##

The type of an asynchronous resource was invalid. Note that users are also able to define their own types if using the public embedder API.

### ERR_BUFFER_OUT_OF_BOUNDS##

An operation outside the bounds of a `Buffer` was attempted.

### ERR_BUFFER_TOO_LARGE##

An attempt has been made to create a `Buffer` larger than the maximum allowed size.

### ERR_CHILD_CLOSED_BEFORE_REPLY##

A child process was closed before the parent received a reply.

### ERR_CONSOLE_WRITABLE_STREAM##

`Console` was instantiated without `stdout` stream, or `Console` has a non-writable `stdout` or `stderr` stream.

### ERR_CPU_USAGE##

The native call from `process.cpuUsage` could not be processed.

### ERR_CRYPTO_CUSTOM_ENGINE_NOT_SUPPORTED##

A client certificate engine was requested that is not supported by the version of OpenSSL being used.

### ERR_CRYPTO_ECDH_INVALID_FORMAT##

An invalid value for the `format` argument was passed to the `crypto.ECDH()` class `getPublicKey()` method.

### ERR_CRYPTO_ENGINE_UNKNOWN##

An invalid crypto engine identifier was passed to `require('crypto').setEngine()`.

### ERR_CRYPTO_FIPS_FORCED##

The `--force-fips` command-line argument was used but there was an attempt to enable or disable FIPS mode in the `crypto` module.

### ERR_CRYPTO_FIPS_UNAVAILABLE##

An attempt was made to enable or disable FIPS mode, but FIPS mode was not available.

### ERR_CRYPTO_HASH_DIGEST_NO_UTF16##

The UTF-16 encoding was used with `hash.digest()`. While the `hash.digest()` method does allow an `encoding` argument to be passed in, causing the method to return a string rather than a `Buffer`, the UTF-16 encoding (e.g. `ucs` or `utf16le`) is not supported.

### ERR_CRYPTO_HASH_FINALIZED##

`hash.digest()` was called multiple times. The `hash.digest()` method must be called no more than one time per instance of a `Hash` object.

### ERR_CRYPTO_HASH_UPDATE_FAILED##

`hash.update()` failed for any reason. This should rarely, if ever, happen.

### ERR_CRYPTO_INVALID_DIGEST##

An invalid crypto digest algorithm was specified.

### ERR_CRYPTO_SIGN_KEY_REQUIRED##

A signing `key` was not provided to the `sign.sign()` method.

### ERR_CRYPTO_TIMING_SAFE_EQUAL_LENGTH##

`crypto.timingSafeEqual()` was called with `Buffer`, `TypedArray`, or `DataView` arguments of different lengths.

### ERR_DNS_SET_SERVERS_FAILED##

`c-ares` failed to set the DNS server.

### ERR_DOMAIN_CALLBACK_NOT_AVAILABLE##

The `domain` module was not usable since it could not establish the required error handling hooks, because `process.setUncaughtExceptionCaptureCallback()` had been called at an earlier point in time.

### ERR_DOMAIN_CANNOT_SET_UNCAUGHT_EXCEPTION_CAPTURE##

`process.setUncaughtExceptionCaptureCallback()` could not be called because the `domain` module has been loaded at an earlier point in time.

The stack trace is extended to include the point in time at which the `domain` module had been loaded.

### ERR_ENCODING_INVALID_ENCODED_DATA##

Data provided to `util.TextDecoder()` API was invalid according to the encoding provided.

### ERR_ENCODING_NOT_SUPPORTED##

Encoding provided to `util.TextDecoder()` API was not one of the WHATWG Supported Encodings.

### ERR_FALSY_VALUE_REJECTION##

A `Promise` that was callbackified via `util.callbackify()` was rejected with a falsy value.

### ERR_HTTP_HEADERS_SENT##

An attempt was made to add more headers after the headers had already been sent.

### ERR_HTTP_INVALID_CHAR##

An invalid character was found in an HTTP response status message (reason phrase).

### ERR_HTTP_INVALID_STATUS_CODE##

Status code was outside the regular status code range (100-999).

### ERR_HTTP_TRAILER_INVALID##

The `Trailer` header was set even though the transfer encoding does not support that.

### ERR_HTTP2_ALREADY_SHUTDOWN##

Occurs with multiple attempts to shutdown an HTTP/2 session.

### ERR_HTTP2_ALTSVC_INVALID_ORIGIN##

HTTP/2 ALTSVC frames require a valid origin.

### ERR_HTTP2_ALTSVC_LENGTH##

HTTP/2 ALTSVC frames are limited to a maximum of 16,382 payload bytes.

### ERR_HTTP2_CONNECT_AUTHORITY##

For HTTP/2 requests using the `CONNECT` method, the `:authority` pseudo-header is required.

### ERR_HTTP2_CONNECT_PATH##

For HTTP/2 requests using the `CONNECT` method, the `:path` pseudo-header is forbidden.

### ERR_HTTP2_CONNECT_SCHEME##

For HTTP/2 requests using the `CONNECT` method, the `:scheme` pseudo-header is forbidden.

### ERR_HTTP2_FRAME_ERROR##

A failure occurred sending an individual frame on the HTTP/2 session.

### ERR_HTTP2_GOAWAY_SESSION##

New HTTP/2 Streams may not be opened after the `Http2Session` has received a `GOAWAY` frame from the connected peer.

### ERR_HTTP2_HEADER_REQUIRED##

A required header was missing in an HTTP/2 message.

### ERR_HTTP2_HEADER_SINGLE_VALUE##

Multiple values were provided for an HTTP/2 header field that was required to have only a single value.

### ERR_HTTP2_HEADERS_AFTER_RESPOND##

An additional headers was specified after an HTTP/2 response was initiated.

### ERR_HTTP2_HEADERS_OBJECT##

An HTTP/2 Headers Object was expected.

### ERR_HTTP2_HEADERS_SENT##

An attempt was made to send multiple response headers.

### ERR_HTTP2_INFO_HEADERS_AFTER_RESPOND##

HTTP/2 Informational headers must only be sent prior to calling the `Http2Stream.prototype.respond()` method.

### ERR_HTTP2_INFO_STATUS_NOT_ALLOWED##

Informational HTTP status codes (`1xx`) may not be set as the response status code on HTTP/2 responses.

### ERR_HTTP2_INVALID_CONNECTION_HEADERS##

HTTP/1 connection specific headers are forbidden to be used in HTTP/2 requests and responses.

### ERR_HTTP2_INVALID_HEADER_VALUE##

An invalid HTTP/2 header value was specified.

### ERR_HTTP2_INVALID_INFO_STATUS##

An invalid HTTP informational status code has been specified. Informational status codes must be an integer between `100` and `199` (inclusive).

### ERR_HTTP2_INVALID_PACKED_SETTINGS_LENGTH##

Input `Buffer` and `Uint8Array` instances passed to the `http2.getUnpackedSettings()` API must have a length that is a multiple of six.

### ERR_HTTP2_INVALID_PSEUDOHEADER##

Only valid HTTP/2 pseudoheaders (`:status`, `:path`, `:authority`, `:scheme`, and `:method`) may be used.

### ERR_HTTP2_INVALID_SESSION##

An action was performed on an `Http2Session` object that had already been destroyed.

### ERR_HTTP2_INVALID_SETTING_VALUE##

An invalid value has been specified for an HTTP/2 setting.

### ERR_HTTP2_INVALID_STREAM##

An operation was performed on a stream that had already been destroyed.

### ERR_HTTP2_MAX_PENDING_SETTINGS_ACK##

Whenever an HTTP/2 `SETTINGS` frame is sent to a connected peer, the peer is required to send an acknowledgment that it has received and applied the new `SETTINGS`. By default, a maximum number of unacknowledged `SETTINGS` frames may be sent at any given time. This error code is used when that limit has been reached.

### ERR_HTTP2_NO_SOCKET_MANIPULATION##

An attempt was made to directly manipulate (read, write, pause, resume, etc.) a socket attached to an `Http2Session`.

### ERR_HTTP2_OUT_OF_STREAMS##

The number of streams created on a single HTTP/2 session reached the maximum limit.

### ERR_HTTP2_PAYLOAD_FORBIDDEN##

A message payload was specified for an HTTP response code for which a payload is forbidden.

### ERR_HTTP2_PING_CANCEL##

An HTTP/2 ping was canceled.

### ERR_HTTP2_PING_LENGTH##

HTTP/2 ping payloads must be exactly 8 bytes in length.

### ERR_HTTP2_PSEUDOHEADER_NOT_ALLOWED##

An HTTP/2 pseudo-header has been used inappropriately. Pseudo-headers are header key names that begin with the `:` prefix.

### ERR_HTTP2_PUSH_DISABLED##

An attempt was made to create a push stream, which had been disabled by the client.

### ERR_HTTP2_SEND_FILE##

An attempt was made to use the `Http2Stream.prototype.responseWithFile()` API to send something other than a regular file.

### ERR_HTTP2_SESSION_ERROR##

The `Http2Session` closed with a non-zero error code.

### ERR_HTTP2_SOCKET_BOUND##

An attempt was made to connect a `Http2Session` object to a `net.Socket` or `tls.TLSSocket` that had already been bound to another `Http2Session` object.

### ERR_HTTP2_STATUS_101##

Use of the `101` Informational status code is forbidden in HTTP/2.

### ERR_HTTP2_STATUS_INVALID##

An invalid HTTP status code has been specified. Status codes must be an integer between `100` and `599` (inclusive).

### ERR_HTTP2_STREAM_CANCEL##

An `Http2Stream` was destroyed before any data was transmitted to the connected peer.

### ERR_HTTP2_STREAM_ERROR##

A non-zero error code was been specified in an `RST_STREAM` frame.

### ERR_HTTP2_STREAM_SELF_DEPENDENCY##

When setting the priority for an HTTP/2 stream, the stream may be marked as a dependency for a parent stream. This error code is used when an attempt is made to mark a stream and dependent of itself.

### ERR_HTTP2_UNSUPPORTED_PROTOCOL##

`http2.connect()` was passed a URL that uses any protocol other than `http:` or `https:`.

### ERR_INDEX_OUT_OF_RANGE##

A given index was out of the accepted range (e.g. negative offsets).

### ERR_INSPECTOR_ALREADY_CONNECTED##

While using the `inspector` module, an attempt was made to connect when the inspector was already connected.

### ERR_INSPECTOR_CLOSED##

While using the `inspector` module, an attempt was made to use the inspector after the session had already closed.

### ERR_INSPECTOR_NOT_AVAILABLE##

The `inspector` module is not available for use.

### ERR_INSPECTOR_NOT_CONNECTED##

While using the `inspector` module, an attempt was made to use the inspector before it was connected.

### ERR_INVALID_ARG_TYPE##

An argument of the wrong type was passed to a Node.js API.

### ERR_INVALID_ARG_VALUE##

An invalid or unsupported value was passed for a given argument.

### ERR_INVALID_ARRAY_LENGTH##

An Array was not of the expected length or in a valid range.

### ERR_INVALID_ASYNC_ID##

An invalid `asyncId` or `triggerAsyncId` was passed using `AsyncHooks`. An id less than -1 should never happen.

### ERR_INVALID_BUFFER_SIZE##

A swap was performed on a `Buffer` but its size was not compatible with the operation.

### ERR_INVALID_CALLBACK##

A callback function was required but was not been provided to a Node.js API.

### ERR_INVALID_CHAR##

Invalid characters were detected in headers.

### ERR_INVALID_CURSOR_POS##

A cursor on a given stream cannot be moved to a specified row without a specified column.

### ERR_INVALID_DOMAIN_NAME##

`hostname` can not be parsed from a provided URL.

### ERR_INVALID_FD##

A file descriptor ('fd') was not valid (e.g. it was a negative value).

### ERR_INVALID_FD_TYPE##

A file descriptor ('fd') type was not valid.

### ERR_INVALID_FILE_URL_HOST##

A Node.js API that consumes `file:` URLs (such as certain functions in the `fs` module) encountered a file URL with an incompatible host. This situation can only occur on Unix-like systems where only `localhost` or an empty host is supported.

### ERR_INVALID_FILE_URL_PATH##

A Node.js API that consumes `file:` URLs (such as certain functions in the `fs` module) encountered a file URL with an incompatible path. The exact semantics for determining whether a path can be used is platform-dependent.

### ERR_INVALID_HANDLE_TYPE##

An attempt was made to send an unsupported "handle" over an IPC communication channel to a child process. See `subprocess.send()` and `process.send()` for more information.

### ERR_INVALID_HTTP_TOKEN##

An invalid HTTP token was supplied.

### ERR_INVALID_IP_ADDRESS##

An IP address is not valid.

### ERR_INVALID_OPT_VALUE##

An invalid or unexpected value was passed in an options object.

### ERR_INVALID_OPT_VALUE_ENCODING##

An invalid or unknown file encoding was passed.

### ERR_INVALID_PERFORMANCE_MARK##

While using the Performance Timing API (`perf_hooks`), a performance mark is invalid.

### ERR_INVALID_PROTOCOL##

An invalid `options.protocol` was passed.

### ERR_INVALID_REPL_EVAL_CONFIG##

Both `breakEvalOnSigint` and `eval` options were set in the REPL config, which is not supported.

### ERR_INVALID_SYNC_FORK_INPUT##

A `Buffer`, `Uint8Array` or `string` was provided as stdio input to a synchronous fork. See the documentation for the `child_process` module for more information.

### ERR_INVALID_THIS##

A Node.js API function was called with an incompatible `this` value.

Example:

    const { URLSearchParams } = require('url');
    const urlSearchParams = new URLSearchParams('foo=bar&baz=new');

    const buf = Buffer.alloc(1);
    urlSearchParams.has.call(buf, 'foo');
    // Throws a TypeError with code 'ERR_INVALID_THIS'

### ERR_INVALID_TUPLE##

An element in the `iterable` provided to the WHATWG `URLSearchParams` constructor did not represent a `[name, value]` tuple – that is, if an element is not iterable, or does not consist of exactly two elements.

### ERR_INVALID_URI##

An invalid URI was passed.

### ERR_INVALID_URL##

An invalid URL was passed to the WHATWG `URL` constructor to be parsed. The thrown error object typically has an additional property `'input'` that contains the URL that failed to parse.

### ERR_INVALID_URL_SCHEME##

An attempt was made to use a URL of an incompatible scheme (protocol) for a specific purpose. It is only used in the WHATWG URL API support in the `fs` module (which only accepts URLs with `'file'` scheme), but may be used in other Node.js APIs as well in the future.

### ERR_IPC_CHANNEL_CLOSED##

An attempt was made to use an IPC communication channel that was already closed.

### ERR_IPC_DISCONNECTED##

An attempt was made to disconnect an IPC communication channel that was already disconnected. See the documentation for the `child_process` module for more information.

### ERR_IPC_ONE_PIPE##

An attempt was made to create a child Node.js process using more than one IPC communication channel. See the documentation for the `child_process` module for more information.

### ERR_IPC_SYNC_FORK##

An attempt was made to open an IPC communication channel with a synchronously forked Node.js process. See the documentation for the `child_process` module for more information.

### ERR_METHOD_NOT_IMPLEMENTED##

A method is required but not implemented.

### ERR_MISSING_ARGS##

A required argument of a Node.js API was not passed. This is only used for strict compliance with the API specification (which in some cases may accept `func(undefined)` but not `func()`). In most native Node.js APIs, `func(undefined)` and `func()` are treated identically, and the `ERR_INVALID_ARG_TYPE` error code may be used instead.

### ERR_MISSING_DYNAMIC_INSTANTIATE_HOOK##

Stability: 1 - Experimental

An ES6 module loader hook specified `format: 'dynamic` but did not provide a `dynamicInstantiate` hook.

### ERR_MISSING_MODULE##

Stability: 1 - Experimental

An ES6 module could not be resolved.

### ERR_MODULE_RESOLUTION_LEGACY##

Stability: 1 - Experimental

A failure occurred resolving imports in an ES6 module.

### ERR_MULTIPLE_CALLBACK##

A callback was called more than once.

Note: A callback is almost always meant to only be called once as the query can either be fulfilled or rejected but not both at the same time. The latter would be possible by calling a callback more than once.

### ERR_NAPI_CONS_FUNCTION##

While using `N-API`, a constructor passed was not a function.

### ERR_NAPI_CONS_PROTOTYPE_OBJECT##

While using `N-API`, `Constructor.prototype` was not an object.

### ERR_NAPI_INVALID_DATAVIEW_ARGS##

While calling `napi_create_dataview()`, a given `offset` was outside the bounds of the dataview or `offset + length` was larger than a length of given `buffer`.

### ERR_NAPI_INVALID_TYPEDARRAY_ALIGNMENT##

While calling `napi_create_typedarray()`, the provided `offset` was not a multiple of the element size.

### ERR_NAPI_INVALID_TYPEDARRAY_LENGTH##

While calling `napi_create_typedarray()`, `(length * size_of_element) + byte_offset` was larger than the length of given `buffer`.

### ERR_NO_CRYPTO##

An attempt was made to use crypto features while Node.js was not compiled with OpenSSL crypto support.

### ERR_NO_ICU##

An attempt was made to use features that require ICU, but Node.js was not compiled with ICU support.

### ERR_NO_LONGER_SUPPORTED##

A Node.js API was called in an unsupported manner.

For example: `Buffer.write(string, encoding, offset[, length])`

### ERR_OUT_OF_RANGE##

An input argument value was outside an acceptable range.

### ERR_PARSE_HISTORY_DATA##

The `REPL` module was unable parse data from the REPL history file.

### ERR_REQUIRE_ESM##

Stability: 1 - Experimental

An attempt was made to `require()` an ES6 module.

### ERR_SERVER_ALREADY_LISTEN##

The `server.listen()` method was called while a `net.Server` was already listening. This applies to all instances of `net.Server`, including HTTP, HTTPS, and HTTP/2 Server instances.

### ERR_SOCKET_ALREADY_BOUND##

An attempt was made to bind a socket that has already been bound.

### ERR_SOCKET_BAD_BUFFER_SIZE##

An invalid (negative) size was passed for either the `recvBufferSize` or `sendBufferSize` options in `dgram.createSocket()`.

### ERR_SOCKET_BAD_PORT##

An API function expecting a port > 0 and < 65536 received an invalid value.

### ERR_SOCKET_BAD_TYPE##

An API function expecting a socket type (`udp4` or `udp6`) received an invalid value.

### ERR_SOCKET_BUFFER_SIZE##

While using `dgram.createSocket()`, the size of the receive or send `Buffer` could not be determined.

### ERR_SOCKET_CANNOT_SEND##

Data could be sent on a socket.

### ERR_SOCKET_CLOSED##

An attempt was made to operate on an already closed socket.

### ERR_SOCKET_DGRAM_NOT_RUNNING##

A call was made and the UDP subsystem was not running.

### ERR_STDERR_CLOSE##

An attempt was made to close the `process.stderr` stream. By design, Node.js does not allow `stdout` or `stderr` streams to be closed by user code.

### ERR_STDOUT_CLOSE##

An attempt was made to close the `process.stdout` stream. By design, Node.js does not allow `stdout` or `stderr` streams to be closed by user code.

### ERR_STREAM_CANNOT_PIPE##

An attempt was made to call `stream.pipe()` on a `Writable` stream.

### ERR_STREAM_NULL_VALUES##

An attempt was made to call `stream.write()` with a `null` chunk.

### ERR_STREAM_PUSH_AFTER_EOF##

An attempt was made to call `stream.push()` after a `null`(EOF) had been pushed to the stream.

### ERR_STREAM_READ_NOT_IMPLEMENTED##

An attempt was made to use a readable stream that did not implement `readable._read()`.

### ERR_STREAM_UNSHIFT_AFTER_END_EVENT##

An attempt was made to call `stream.unshift()` after the `end` event was emitted.

### ERR_STREAM_WRAP##

Prevents an abort if a string decoder was set on the Socket or if the decoder is in `objectMode`.

Example

    const Socket = require('net').Socket;
    const instance = new Socket();

    instance.setEncoding('utf8');

### ERR_STREAM_WRITE_AFTER_END##

An attempt was made to call `stream.write()` after `stream.end()` has been called.

### ERR_TLS_CERT_ALTNAME_INVALID##

While using TLS, the hostname/IP of the peer did not match any of the subjectAltNames in its certificate.

### ERR_TLS_DH_PARAM_SIZE##

While using TLS, the parameter offered for the Diffie-Hellman (`DH`) key-agreement protocol is too small. By default, the key length must be greater than or equal to 1024 bits to avoid vulnerabilities, even though it is strongly recommended to use 2048 bits or larger for stronger security.

### ERR_TLS_HANDSHAKE_TIMEOUT##

A TLS/SSL handshake timed out. In this case, the server must also abort the connection.

### ERR_TLS_RENEGOTIATION_FAILED##

A TLS renegotiation request has failed in a non-specific way.

### ERR_TLS_REQUIRED_SERVER_NAME##

While using TLS, the `server.addContext()` method was called without providing a hostname in the first parameter.

### ERR_TLS_SESSION_ATTACK##

An excessive amount of TLS renegotiations is detected, which is a potential vector for denial-of-service attacks.

### ERR_TRANSFORM_ALREADY_TRANSFORMING##

A Transform stream finished while it was still transforming.

### ERR_TRANSFORM_WITH_LENGTH_0##

A Transform stream finished with data still in the write buffer.

### ERR_UNCAUGHT_EXCEPTION_CAPTURE_ALREADY_SET##

`process.setUncaughtExceptionCaptureCallback()` was called twice, without first resetting the callback to `null`.

This error is designed to prevent accidentally overwriting a callback registered from another module.

### ERR_UNESCAPED_CHARACTERS##

A string that contained unescaped characters was received.

### ERR_UNHANDLED_ERROR##

An unhandled error occurred (for instance, when an `'error'` event is emitted by an `EventEmitter` but an `'error'` handler is not registered).

### ERR_UNKNOWN_ENCODING##

An invalid or unknown encoding option was passed to an API.

### ERR_UNKNOWN_FILE_EXTENSION##

Stability: 1 - Experimental

An attempt was made to load a module with an unknown or unsupported file extension.

### ERR_UNKNOWN_MODULE_FORMAT##

Stability: 1 - Experimental

An attempt was made to load a module with an unknown or unsupported format.

### ERR_UNKNOWN_SIGNAL##

An invalid or unknown process signal was passed to an API expecting a valid signal (such as `subprocess.kill()`).

### ERR_UNKNOWN_STDIN_TYPE##

An attempt was made to launch a Node.js process with an unknown `stdin` file type. This error is usually an indication of a bug within Node.js itself, although it is possible for user code to trigger it.

### ERR_UNKNOWN_STREAM_TYPE##

An attempt was made to launch a Node.js process with an unknown `stdout` or `stderr` file type. This error is usually an indication of a bug within Node.js itself, although it is possible for user code to trigger it.

### ERR_V8BREAKITERATOR##

The V8 BreakIterator API was used but the full ICU data set is not installed.

### ERR_VALID_PERFORMANCE_ENTRY_TYPE##

While using the Performance Timing API (`perf_hooks`), no valid performance entry types were found.

### ERR_VALUE_OUT_OF_RANGE##

A given value is out of the accepted range.

### ERR_VM_MODULE_ALREADY_LINKED##

The module attempted to be linked is not eligible for linking, because of one of the following reasons:

- It has already been linked (`linkingStatus` is `'linked'`)
- It is being linked (`linkingStatus` is `'linking'`)
- Linking has failed for this module (`linkingStatus` is `'errored'`)

### ERR_VM_MODULE_DIFFERENT_CONTEXT##

The module being returned from the linker function is from a different context than the parent module. Linked modules must share the same context.

### ERR_VM_MODULE_LINKING_ERRORED##

The linker function returned a module for which linking has failed.

### ERR_VM_MODULE_NOT_LINKED##

The module must be successfully linked before instantiation.

### ERR_VM_MODULE_NOT_MODULE##

The fulfilled value of a linking promise is not a `vm.Module` object.

### ERR_VM_MODULE_STATUS##

The current module's status does not allow for this operation. The specific meaning of the error depends on the specific function.

### ERR_ZLIB_BINDING_CLOSED##

An attempt was made to use a `zlib` object after it has already been closed.

### ERR_ZLIB_INITIALIZATION_FAILED##

Creation of a `zlib` object failed due to incorrect configuration.