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.

Node.js style callbacks

Most asynchronous methods exposed by the Node.js core API follow an idiomatic pattern 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 nodeStyleCallback(err, data) {
  if (err) {
    console.error('There was an error', err);
    return;
  }
  console.log(data);
}

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

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 a Node.js style 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.

It is important to note that 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

Used generically to identify that an iterable argument (i.e. a value that works with for...of loops) is required, but not provided to a Node.js API.

ERR_ASSERTION

Used as 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

Used with AsyncHooks to indicate an attempt of registering something that is not a function as a callback.

ERR_ASYNC_TYPE

Used when the type of an asynchronous resource is invalid. Note that users are also able to define their own types when using the public embedder API.

ERR_BUFFER_OUT_OF_BOUNDS

Used when attempting to perform an operation outside the bounds of a Buffer.

ERR_BUFFER_TOO_LARGE

Used when an attempt has been made to create a Buffer larger than the maximum allowed size.

ERR_CHILD_CLOSED_BEFORE_REPLY

Used when a child process is closed before the parent received a reply.

ERR_CONSOLE_WRITABLE_STREAM

Used when Console is instantiated without stdout stream or when stdout or stderr streams are not writable.

ERR_CPU_USAGE

Used when the native call from process.cpuUsage cannot be processed properly.

ERR_CRYPTO_ECDH_INVALID_FORMAT

Used when an invalid value for the format argument has been passed to the crypto.ECDH() class getPublicKey() method.

ERR_CRYPTO_ENGINE_UNKNOWN

Used when an invalid crypto engine identifier is passed to require('crypto').setEngine().

ERR_CRYPTO_FIPS_FORCED

Used when trying to enable or disable FIPS mode in the crypto module and the --force-fips command-line argument is used.

ERR_CRYPTO_FIPS_UNAVAILABLE

Used when trying to enable or disable FIPS mode when FIPS is not available.

ERR_CRYPTO_HASH_DIGEST_NO_UTF16

Used when the UTF-16 encoding is 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

Used when hash.digest() is 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

Used when hash.update() fails for any reason. This should rarely, if ever, happen.

ERR_CRYPTO_INVALID_DIGEST

Used when an invalid crypto digest algorithm is specified.

ERR_CRYPTO_SIGN_KEY_REQUIRED

Used when a signing key is not provided to the sign.sign() method.

ERR_CRYPTO_TIMING_SAFE_EQUAL_LENGTH

Used when calling crypto.timingSafeEqual() with Buffer, TypedArray, or DataView arguments of different lengths.

ERR_DNS_SET_SERVERS_FAILED

Used when c-ares failed to set the DNS server.

ERR_ENCODING_INVALID_ENCODED_DATA

Used by the util.TextDecoder() API when the data provided is invalid according to the encoding provided.

ERR_ENCODING_NOT_SUPPORTED

Used by the util.TextDecoder() API when the encoding provided is not one of the WHATWG Supported Encodings.

ERR_FALSY_VALUE_REJECTION

Used by the util.callbackify() API when a callbackified Promise is rejected with a falsy value (e.g. null).

ERR_HTTP_HEADERS_SENT

Used when headers have already been sent and another attempt is made to add more headers.

ERR_HTTP_INVALID_CHAR

Used when an invalid character is found in an HTTP response status message (reason phrase).

ERR_HTTP_INVALID_STATUS_CODE

Used for status codes outside the regular status code ranges (100-999).

ERR_HTTP_TRAILER_INVALID

Used when the Trailer header is set even though the transfer encoding does not support that.

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

Used when a failure occurs sending an individual frame on the HTTP/2 session.

ERR_HTTP2_HEADER_REQUIRED

Used when a required header is missing in an HTTP/2 message.

ERR_HTTP2_HEADER_SINGLE_VALUE

Used when multiple values have been provided for an HTTP header field that required to have only a single value.

ERR_HTTP2_HEADERS_AFTER_RESPOND

Used when trying to specify additional headers after an HTTP/2 response initiated.

ERR_HTTP2_HEADERS_OBJECT

Used when an HTTP/2 Headers Object is expected.

ERR_HTTP2_HEADERS_SENT

Used when an attempt is 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

Used to indicate that an invalid HTTP/2 header value has been 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

Used when any action is performed on an Http2Session object that has already been destroyed.

ERR_HTTP2_INVALID_SETTING_VALUE

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

ERR_HTTP2_INVALID_STREAM

Used when an operation has been performed on a stream that has 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 acknowledgement that it has received and applied the new SETTINGS. By default, a maximum number of un-acknowledged SETTINGS frame may be sent at any given time. This error code is used when that limit has been reached.

ERR_HTTP2_NO_SOCKET_MANIPULATION

Used when attempting to directly manipulate (e.g read, write, pause, resume, etc.) a socket attached to an Http2Session.

ERR_HTTP2_OUT_OF_STREAMS

Used when the maximum number of streams on a single HTTP/2 session have been created.

ERR_HTTP2_PAYLOAD_FORBIDDEN

Used when a message payload is specified for an HTTP response code for which a payload is forbidden.

ERR_HTTP2_PSEUDOHEADER_NOT_ALLOWED

Used to indicate that an HTTP/2 pseudo-header has been used inappropriately. Pseudo-headers are header key names that begin with the : prefix.

ERR_HTTP2_PUSH_DISABLED

Used when push streams have been disabled by the client but an attempt to create a push stream is made.

ERR_HTTP2_SEND_FILE

Used when an attempt is made to use the Http2Stream.prototype.responseWithFile() API to send a non-regular file.

ERR_HTTP2_SOCKET_BOUND

Used when an attempt is made to connect a Http2Session object to a net.Socket or tls.TLSSocket that has 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_CLOSED

Used when an action has been performed on an HTTP/2 Stream that has already been closed.

ERR_HTTP2_STREAM_ERROR

Used when a non-zero error code has 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

Used when http2.connect() is passed a URL that uses any protocol other than http: or https:.

ERR_INDEX_OUT_OF_RANGE

Used when a given index is out of the accepted range (e.g. negative offsets).

ERR_INSPECTOR_ALREADY_CONNECTED

When using the inspector module, the ERR_INSPECTOR_ALREADY_CONNECTED error code is used when an attempt is made to connect when the inspector is already connected.

ERR_INSPECTOR_CLOSED

When using the inspector module, the ERR_INSPECTOR_CLOSED error code is used when an attempt is made to use the inspector after the session has already closed.

ERR_INSPECTOR_NOT_AVAILABLE

Used to identify when the inspector module is not available for use.

ERR_INSPECTOR_NOT_CONNECTED

When using the inspector module, the ERR_INSPECTOR_NOT_CONNECTED error code is used when an attempt is made to use the inspector before it is connected.

ERR_INVALID_ARG_TYPE

Used generically to identify that an argument of the wrong type has been passed to a Node.js API.

ERR_INVALID_ARG_VALUE

Used generically to identify that an invalid or unsupported value has been passed for a given argument.

ERR_INVALID_ARRAY_LENGTH

Used when an Array is not of the expected length or in a valid range.

ERR_INVALID_ASYNC_ID

Used with AsyncHooks when an invalid asyncId or triggerAsyncId is passed. An id less than -1 should never happen.

ERR_INVALID_BUFFER_SIZE

Used when performing a swap on a Buffer but it's size is not compatible with the operation.

ERR_INVALID_CALLBACK

Used generically to identify that a callback function is required and has not been provided to a Node.js API.

ERR_INVALID_CHAR

Used when invalid characters are detected in headers.

ERR_INVALID_CURSOR_POS

The 'ERR_INVALID_CURSOR_POS' is thrown specifically when a cursor on a given stream is attempted to move to a specified row without a specified column.

ERR_INVALID_DOMAIN_NAME

Used when hostname can not be parsed from a provided URL.

ERR_INVALID_FD

Used when a file descriptor ('fd') is not valid (e.g. it has a negative value).

ERR_INVALID_FD_TYPE

Used when a file descriptor ('fd') type is not valid.

ERR_INVALID_FILE_URL_HOST

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

ERR_INVALID_FILE_URL_PATH

Used when a Node.js API that consumes file: URLs (such as certain functions in the fs module) encounters 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

Used when an attempt is 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

Used when options.method received an invalid HTTP token.

ERR_INVALID_IP_ADDRESS

Used when an IP address is not valid.

ERR_INVALID_OPT_VALUE

Used generically to identify when an invalid or unexpected value has been passed in an options object.

ERR_INVALID_OPT_VALUE_ENCODING

Used when an invalid or unknown file encoding is passed.

ERR_INVALID_PERFORMANCE_MARK

Used by the Performance Timing API (perf_hooks) when a performance mark is invalid.

ERR_INVALID_PROTOCOL

Used when an invalid options.protocol is passed.

ERR_INVALID_REPL_EVAL_CONFIG

Used when both breakEvalOnSigint and eval options are set in the REPL config, which is not supported.

ERR_INVALID_SYNC_FORK_INPUT

Used when a Buffer, Uint8Array or string is provided as stdio input to a synchronous fork. See the documentation for the child_process module for more information.

ERR_INVALID_THIS

Used generically to identify that a Node.js API function is 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

Used when an element in the iterable provided to the WHATWG URLSearchParams constructor does 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

Used when an invalid URI is passed.

ERR_INVALID_URL

Used when an invalid URL is 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

Used generically to signify an attempt to use a URL of an incompatible scheme (aka protocol) for a specific purpose. It is currently 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

Used when an attempt is made to use an IPC communication channel that has already been closed.

ERR_IPC_DISCONNECTED

Used when an attempt is made to disconnect an already disconnected IPC communication channel between two Node.js processes. See the documentation for the child_process module for more information.

ERR_IPC_ONE_PIPE

Used when an attempt is 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

Used when an attempt is made to open an IPC communication channel with a synchronous forked Node.js process. See the documentation for the child_process module for more information.

ERR_METHOD_NOT_IMPLEMENTED

Used when a method is required but not implemented.

ERR_MISSING_ARGS

Used when a required argument of a Node.js API is 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_MODULE

Stability: 1 - Experimental

Used when an ES6 module cannot be resolved.

ERR_MODULE_RESOLUTION_LEGACY

Stability: 1 - Experimental

Used when a failure occurs resolving imports in an ES6 module.

ERR_MULTIPLE_CALLBACK

Used when a callback is called more then 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 then once.

ERR_NAPI_CONS_FUNCTION

Used by the N-API when a constructor passed is not a function.

ERR_NAPI_CONS_PROTOTYPE_OBJECT

Used by the N-API when Constructor.prototype is not an object.

ERR_NO_CRYPTO

Used when an attempt is made to use crypto features while Node.js is not compiled with OpenSSL crypto support.

ERR_NO_ICU

Used when an attempt is made to use features that require ICU, while Node.js is not compiled with ICU support.

ERR_NO_LONGER_SUPPORTED

Used when a Node.js API is called in an unsupported manner.

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

ERR_OUTOFMEMORY

Used generically to identify that an operation caused an out of memory condition.

ERR_OUT_OF_RANGE

Used generically when an input argument value values outside an acceptable range.

ERR_PARSE_HISTORY_DATA

Used by the REPL module when it cannot parse data from the REPL history file.

ERR_REQUIRE_ESM

Stability: 1 - Experimental

Used when an attempt is made to require() an ES6 module.

ERR_SERVER_ALREADY_LISTEN

Used when the server.listen() method is called while a net.Server is already listening. This applies to all instances of net.Server, including HTTP, HTTPS, and HTTP/2 Server instances.

ERR_SOCKET_ALREADY_BOUND

Used when an attempt is made to bind a socket that has already been bound.

ERR_SOCKET_BAD_BUFFER_SIZE

Used when an invalid (negative) size is passed for either the recvBufferSize or sendBufferSize options in dgram.createSocket().

ERR_SOCKET_BAD_PORT

Used when an API function expecting a port > 0 and < 65536 receives an invalid value.

ERR_SOCKET_BAD_TYPE

Used when an API function expecting a socket type (udp4 or udp6) receives an invalid value.

ERR_SOCKET_BUFFER_SIZE

Used when using dgram.createSocket() and the size of the receive or send Buffer cannot be determined.

ERR_SOCKET_CANNOT_SEND

Used when data cannot be sent on a socket.

ERR_SOCKET_CLOSED

Used when an attempt is made to operate on an already closed socket.

ERR_SOCKET_DGRAM_NOT_RUNNING

Used when a call is made and the UDP subsystem is not running.

ERR_STDERR_CLOSE

Used when an attempt is 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

Used when an attempt is 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_PUSH_AFTER_EOF

Used when an attempt is made to call stream.push() after a null(EOF) has been pushed to the stream.

ERR_STREAM_READ_NOT_IMPLEMENTED

Used when an attempt is made to use a readable stream that has not implemented readable._read().

ERR_STREAM_UNSHIFT_AFTER_END_EVENT

Used when an attempt is made to call stream.unshift() after the end event has been emitted.

ERR_STREAM_WRAP

Used to prevent an abort if a string decoder was set on the Socket or if in objectMode.

Example

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

instance.setEncoding('utf8');

ERR_TLS_CERT_ALTNAME_INVALID

Used with TLS, when the hostname/IP of the peer does not match any of the subjectAltNames in its certificate.

ERR_TLS_DH_PARAM_SIZE

Used with TLS when 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 error emitted by the server whenever a TLS/SSL handshake times out. In this case, the server must also abort the connection.

ERR_TLS_RENEGOTIATION_FAILED

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

ERR_TLS_REQUIRED_SERVER_NAME

Used with TLS, when calling the server.addContext() method without providing a hostname in the first parameter.

ERR_TLS_SESSION_ATTACK

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

ERR_TRANSFORM_ALREADY_TRANSFORMING

Used in Transform streams when the stream finishes while it is still transforming.

ERR_TRANSFORM_WITH_LENGTH_0

Used in Transform streams when the stream finishes with data still in the write buffer.

ERR_UNESCAPED_CHARACTERS

Used when a string that contains unescaped characters was received.

ERR_UNHANDLED_ERROR

Used when an unhandled "error" occurs (for instance, when an 'error' event is emitted by an EventEmitter but an 'error' handler is not registered).

ERR_UNKNOWN_ENCODING

Used when an invalid or unknown encoding option is passed to an API.

ERR_UNKNOWN_FILE_EXTENSION

Stability: 1 - Experimental

Used when attempting to load a module with an unknown or unsupported file extension.

ERR_UNKNOWN_MODULE_FORMAT

Stability: 1 - Experimental

Used when attempting to load a module with an unknown or unsupported format.

ERR_UNKNOWN_SIGNAL

Used when an invalid or unknown process signal is passed to an API expecting a valid signal (such as subprocess.kill()).

ERR_UNKNOWN_STDIN_TYPE

Used when an attempt is made to launch a Node.js process with an unknown stdin file type. Errors of this kind cannot typically be caused by errors in user code, although it is not impossible. Occurrences of this error are most likely an indication of a bug within Node.js itself.

ERR_UNKNOWN_STREAM_TYPE

Used when an attempt is made to launch a Node.js process with an unknown stdout or stderr file type. Errors of this kind cannot typically be caused by errors in user code, although it is not impossible. Occurrences of this error are most likely an indication of a bug within Node.js itself.

ERR_V8BREAKITERATOR

Used when the V8 BreakIterator API is used but the full ICU data set is not installed.

ERR_VALID_PERFORMANCE_ENTRY_TYPE

Used by the Performance Timing API (perf_hooks) when no valid performance entry types were found.

ERR_VALUE_OUT_OF_RANGE

Used when a given value is out of the accepted range.

ERR_ZLIB_BINDING_CLOSED

Used when an attempt is made to use a zlib object after it has already been closed.

ERR_ZLIB_INITIALIZATION_FAILED

Used when creation of a zlib object fails due to incorrect configuration.

Files

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Errors

Error Propagation and Interception

Node.js style callbacks

Class: Error

new Error(message)

Error.captureStackTrace(targetObject[, constructorOpt])

Error.stackTraceLimit

error.code

error.message

error.stack

Class: AssertionError

Class: RangeError

Class: ReferenceError

Class: SyntaxError

Class: TypeError

Exceptions vs. Errors

System Errors

Class: System Error

error.code

error.errno

error.syscall

error.path

error.address

error.port

Common System Errors

Node.js Error Codes

ERR_ARG_NOT_ITERABLE

ERR_ASSERTION

ERR_ASYNC_CALLBACK

ERR_ASYNC_TYPE

ERR_BUFFER_OUT_OF_BOUNDS

ERR_BUFFER_TOO_LARGE

ERR_CHILD_CLOSED_BEFORE_REPLY

ERR_CONSOLE_WRITABLE_STREAM

ERR_CPU_USAGE

ERR_CRYPTO_ECDH_INVALID_FORMAT

ERR_CRYPTO_ENGINE_UNKNOWN

ERR_CRYPTO_FIPS_FORCED

ERR_CRYPTO_FIPS_UNAVAILABLE

ERR_CRYPTO_HASH_DIGEST_NO_UTF16

ERR_CRYPTO_HASH_FINALIZED

ERR_CRYPTO_HASH_UPDATE_FAILED

ERR_CRYPTO_INVALID_DIGEST

ERR_CRYPTO_SIGN_KEY_REQUIRED

ERR_CRYPTO_TIMING_SAFE_EQUAL_LENGTH

ERR_DNS_SET_SERVERS_FAILED

ERR_ENCODING_INVALID_ENCODED_DATA

ERR_ENCODING_NOT_SUPPORTED

ERR_FALSY_VALUE_REJECTION

ERR_HTTP_HEADERS_SENT

ERR_HTTP_INVALID_CHAR

ERR_HTTP_INVALID_STATUS_CODE

ERR_HTTP_TRAILER_INVALID

ERR_HTTP2_CONNECT_AUTHORITY

ERR_HTTP2_CONNECT_PATH

ERR_HTTP2_CONNECT_SCHEME

ERR_HTTP2_FRAME_ERROR

ERR_HTTP2_HEADER_REQUIRED

ERR_HTTP2_HEADER_SINGLE_VALUE

ERR_HTTP2_HEADERS_AFTER_RESPOND

ERR_HTTP2_HEADERS_OBJECT

ERR_HTTP2_HEADERS_SENT

ERR_HTTP2_INFO_HEADERS_AFTER_RESPOND

ERR_HTTP2_INFO_STATUS_NOT_ALLOWED

ERR_HTTP2_INVALID_CONNECTION_HEADERS

ERR_HTTP2_INVALID_HEADER_VALUE

ERR_HTTP2_INVALID_INFO_STATUS

ERR_HTTP2_INVALID_PACKED_SETTINGS_LENGTH

ERR_HTTP2_INVALID_PSEUDOHEADER

ERR_HTTP2_INVALID_SESSION

ERR_HTTP2_INVALID_SETTING_VALUE

ERR_HTTP2_INVALID_STREAM

ERR_HTTP2_MAX_PENDING_SETTINGS_ACK

ERR_HTTP2_NO_SOCKET_MANIPULATION