Deprecated APIs | Node.js v10.2.0 Documentation

Node.js

- About these Docs
- Usage & Example

- Assertion Testing
- Async Hooks
- Buffer
- C++ Addons
- C/C++ Addons - N-API
- Child Processes
- Cluster
- Command Line Options
- Console
- Crypto
- Debugger
- Deprecated APIs
- DNS
- Domain
- ECMAScript Modules
- Errors
- Events
- File System
- Globals
- HTTP
- HTTP/2
- HTTPS
- Inspector
- Internationalization
- Modules
- Net
- OS
- Path
- Performance Hooks
- Process
- Punycode
- Query Strings
- Readline
- REPL
- Stream
- String Decoder
- Timers
- TLS/SSL
- Trace Events
- TTY
- UDP/Datagram
- URL
- Utilities
- V8
- VM
- ZLIB

- GitHub Repo & Issue Tracker
- Mailing List

# Deprecated APIs#

Node.js may deprecate APIs when either: (a) use of the API is considered to be unsafe, (b) an improved alternative API has been made available, or (c) breaking changes to the API are expected in a future major release.

Node.js utilizes three kinds of Deprecations:

- Documentation-only
- Runtime
- End-of-Life

A Documentation-only deprecation is one that is expressed only within the Node.js API docs. These generate no side-effects while running Node.js. Some Documentation-only deprecations trigger a runtime warning when launched with `--pending-deprecation` flag (or its alternative, `NODE_PENDING_DEPRECATION=1` environment variable), similarly to Runtime deprecations below. Documentation-only deprecations that support that flag are explicitly labeled as such in the list of Deprecated APIs.

A Runtime deprecation will, by default, generate a process warning that will be printed to `stderr` the first time the deprecated API is used. When the `--throw-deprecation` command-line flag is used, a Runtime deprecation will cause an error to be thrown.

An End-of-Life deprecation is used to identify code that either has been removed or will soon be removed from Node.js.

## Revoking deprecations#

Occasionally, the deprecation of an API may be reversed. In such situations, this document will be updated with information relevant to the decision. However, the deprecation identifier will not be modified.

## List of Deprecated APIs#

### DEP0001: http.OutgoingMessage.prototype.flush#

Type: Runtime

The `OutgoingMessage.prototype.flush()` method is deprecated. Use `OutgoingMessage.prototype.flushHeaders()` instead.

### DEP0002: require('_linklist')#

Type: End-of-Life

The `_linklist` module is deprecated. Please use a userland alternative.

### DEP0003: _writableState.buffer#

Type: Runtime

The `_writableState.buffer` property is deprecated. Use the `_writableState.getBuffer()` method instead.

### DEP0004: CryptoStream.prototype.readyState#

Type: Documentation-only

The `CryptoStream.prototype.readyState` property is deprecated and should not be used.

### DEP0005: Buffer() constructor#

Type: Runtime (supports `--pending-deprecation`)

The `Buffer()` function and `new Buffer()` constructor are deprecated due to API usability issues that can potentially lead to accidental security issues.

As an alternative, use of the following methods of constructing `Buffer` objects is strongly recommended:

- `Buffer.alloc(size[, fill[, encoding]])` - Create a `Buffer` with initialized memory.
- `Buffer.allocUnsafe(size)` - Create a `Buffer` with uninitialized memory.
- `Buffer.allocUnsafeSlow(size)` - Create a `Buffer` with uninitialized memory.
- `Buffer.from(array)` - Create a `Buffer` with a copy of `array`
- `Buffer.from(arrayBuffer[, byteOffset[, length]])` - Create a `Buffer` that wraps the given `arrayBuffer`.
- `Buffer.from(buffer)` - Create a `Buffer` that copies `buffer`.
- `Buffer.from(string[, encoding])` - Create a `Buffer` that copies `string`.

As of v10.0.0, a deprecation warning is printed at runtime when `--pending-deprecation` is used or when the calling code is outside `node_modules` in order to better target developers, rather than users.

### DEP0006: child_process options.customFds#

Type: Runtime

Within the `child_process` module's `spawn()`, `fork()`, and `exec()` methods, the `options.customFds` option is deprecated. The `options.stdio` option should be used instead.

### DEP0007: Replace cluster worker.suicide with worker.exitedAfterDisconnect#

Type: End-of-Life

In an earlier version of the Node.js `cluster`, a boolean property with the name `suicide` was added to the `Worker` object. The intent of this property was to provide an indication of how and why the `Worker` instance exited. In Node.js 6.0.0, the old property was deprecated and replaced with a new `worker.exitedAfterDisconnect` property. The old property name did not precisely describe the actual semantics and was unnecessarily emotion-laden.

### DEP0008: require('constants')#

Type: Documentation-only

The `constants` module has been deprecated. When requiring access to constants relevant to specific Node.js builtin modules, developers should instead refer to the `constants` property exposed by the relevant module. For instance, `require('fs').constants` and `require('os').constants`.

### DEP0009: crypto.pbkdf2 without digest#

Type: End-of-Life

Use of the `crypto.pbkdf2()` API without specifying a digest was deprecated in Node.js 6.0 because the method defaulted to using the non-recommended `'SHA1'` digest. Previously, a deprecation warning was printed. Starting in Node.js 8.0.0, calling `crypto.pbkdf2()` or `crypto.pbkdf2Sync()` with an undefined `digest` will throw a `TypeError`.

### DEP0010: crypto.createCredentials#

Type: Runtime

The `crypto.createCredentials()` API is deprecated. Please use `tls.createSecureContext()` instead.

### DEP0011: crypto.Credentials#

Type: Runtime

The `crypto.Credentials` class is deprecated. Please use `tls.SecureContext` instead.

### DEP0012: Domain.dispose#

Type: End-of-Life

`Domain.dispose()` has been removed. Recover from failed I/O actions explicitly via error event handlers set on the domain instead.

### DEP0013: fs asynchronous function without callback#

Type: End-of-Life

Calling an asynchronous function without a callback throws a `TypeError` in Node.js 10.0.0 onwards. (See https://github.com/nodejs/node/pull/12562.)

### DEP0014: fs.read legacy String interface#

Type: End-of-Life

The `fs.read()` legacy `String` interface is deprecated. Use the `Buffer` API as mentioned in the documentation instead.

### DEP0015: fs.readSync legacy String interface#

Type: End-of-Life

The `fs.readSync()` legacy `String` interface is deprecated. Use the `Buffer` API as mentioned in the documentation instead.

### DEP0016: GLOBAL/root#

Type: Runtime

The `GLOBAL` and `root` aliases for the `global` property have been deprecated and should no longer be used.

### DEP0017: Intl.v8BreakIterator#

Type: End-of-Life

`Intl.v8BreakIterator` was a non-standard extension and has been removed. See `Intl.Segmenter`.

### DEP0018: Unhandled promise rejections#

Type: Runtime

Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

### DEP0019: require('.') resolved outside directory#

Type: Runtime

In certain cases, `require('.')` may resolve outside the package directory. This behavior is deprecated and will be removed in a future major Node.js release.

### DEP0020: Server.connections#

Type: Runtime

The `Server.connections` property is deprecated. Please use the `Server.getConnections()` method instead.

### DEP0021: Server.listenFD#

Type: Runtime

The `Server.listenFD()` method is deprecated. Please use `Server.listen({fd: <number>})` instead.

### DEP0022: os.tmpDir()#

Type: Runtime

The `os.tmpDir()` API is deprecated. Please use `os.tmpdir()` instead.

### DEP0023: os.getNetworkInterfaces()#

Type: Runtime

The `os.getNetworkInterfaces()` method is deprecated. Please use the `os.networkInterfaces` property instead.

### DEP0024: REPLServer.prototype.convertToContext()#

Type: End-of-Life

The `REPLServer.prototype.convertToContext()` API is deprecated and should not be used.

### DEP0025: require('sys')#

Type: Runtime

The `sys` module is deprecated. Please use the `util` module instead.

### DEP0026: util.print()#

Type: Runtime

The `util.print()` API is deprecated. Please use `console.log()` instead.

### DEP0027: util.puts()#

Type: Runtime

The `util.puts()` API is deprecated. Please use `console.log()` instead.

### DEP0028: util.debug()#

Type: Runtime

The `util.debug()` API is deprecated. Please use `console.error()` instead.

### DEP0029: util.error()#

Type: Runtime

The `util.error()` API is deprecated. Please use `console.error()` instead.

### DEP0030: SlowBuffer#

Type: Documentation-only

The `SlowBuffer` class has been deprecated. Please use `Buffer.allocUnsafeSlow(size)` instead.

### DEP0031: ecdh.setPublicKey()#

Type: Documentation-only

The `ecdh.setPublicKey()` method is now deprecated as its inclusion in the API is not useful.

### DEP0032: domain module#

Type: Documentation-only

The `domain` module is deprecated and should not be used.

### DEP0033: EventEmitter.listenerCount()#

Type: Documentation-only

The `EventEmitter.listenerCount(emitter, eventName)` API has been deprecated. Please use `emitter.listenerCount(eventName)` instead.

### DEP0034: fs.exists(path, callback)#

Type: Documentation-only

The `fs.exists(path, callback)` API has been deprecated. Please use `fs.stat()` or `fs.access()` instead.

### DEP0035: fs.lchmod(path, mode, callback)#

Type: Documentation-only

The `fs.lchmod(path, mode, callback)` API has been deprecated.

### DEP0036: fs.lchmodSync(path, mode)#

Type: Documentation-only

The `fs.lchmodSync(path, mode)` API has been deprecated.

### DEP0037: fs.lchown(path, uid, gid, callback)#

Type: Documentation-only

The `fs.lchown(path, uid, gid, callback)` API has been deprecated.

### DEP0038: fs.lchownSync(path, uid, gid)#

Type: Documentation-only

The `fs.lchownSync(path, uid, gid)` API has been deprecated.

### DEP0039: require.extensions#

Type: Documentation-only

The `require.extensions` property has been deprecated.

### DEP0040: punycode module#

Type: Documentation-only

The `punycode` module has been deprecated. Please use a userland alternative instead.

### DEP0041: NODE_REPL_HISTORY_FILE environment variable#

Type: End-of-Life

The `NODE_REPL_HISTORY_FILE` environment variable was removed. Please use `NODE_REPL_HISTORY` instead.

### DEP0042: tls.CryptoStream#

Type: Documentation-only

The `tls.CryptoStream` class has been deprecated. Please use `tls.TLSSocket` instead.

### DEP0043: tls.SecurePair#

Type: Documentation-only

The `tls.SecurePair` class has been deprecated. Please use `tls.TLSSocket` instead.

### DEP0044: util.isArray()#

Type: Documentation-only

The `util.isArray()` API has been deprecated. Please use `Array.isArray()` instead.

### DEP0045: util.isBoolean()#

Type: Documentation-only

The `util.isBoolean()` API has been deprecated.

### DEP0046: util.isBuffer()#

Type: Documentation-only

The `util.isBuffer()` API has been deprecated. Please use `Buffer.isBuffer()` instead.

### DEP0047: util.isDate()#

Type: Documentation-only

The `util.isDate()` API has been deprecated.

### DEP0048: util.isError()#

Type: Documentation-only

The `util.isError()` API has been deprecated.

### DEP0049: util.isFunction()#

Type: Documentation-only

The `util.isFunction()` API has been deprecated.

### DEP0050: util.isNull()#

Type: Documentation-only

The `util.isNull()` API has been deprecated.

### DEP0051: util.isNullOrUndefined()#

Type: Documentation-only

The `util.isNullOrUndefined()` API has been deprecated.

### DEP0052: util.isNumber()#

Type: Documentation-only

The `util.isNumber()` API has been deprecated.

### DEP0053 util.isObject()#

Type: Documentation-only

The `util.isObject()` API has been deprecated.

### DEP0054: util.isPrimitive()#

Type: Documentation-only

The `util.isPrimitive()` API has been deprecated.

### DEP0055: util.isRegExp()#

Type: Documentation-only

The `util.isRegExp()` API has been deprecated.

### DEP0056: util.isString()#

Type: Documentation-only

The `util.isString()` API has been deprecated.

### DEP0057: util.isSymbol()#

Type: Documentation-only

The `util.isSymbol()` API has been deprecated.

### DEP0058: util.isUndefined()#

Type: Documentation-only

The `util.isUndefined()` API has been deprecated.

### DEP0059: util.log()#

Type: Documentation-only

The `util.log()` API has been deprecated.

### DEP0060: util._extend()#

Type: Documentation-only

The `util._extend()` API has been deprecated.

### DEP0061: fs.SyncWriteStream#

Type: Runtime

The `fs.SyncWriteStream` class was never intended to be a publicly accessible API. No alternative API is available. Please use a userland alternative.

### DEP0062: node --debug#

Type: Runtime

`--debug` activates the legacy V8 debugger interface, which has been removed as of V8 5.8. It is replaced by Inspector which is activated with `--inspect` instead.

### DEP0063: ServerResponse.prototype.writeHeader()#

Type: Documentation-only

The `http` module `ServerResponse.prototype.writeHeader()` API has been deprecated. Please use `ServerResponse.prototype.writeHead()` instead.

The `ServerResponse.prototype.writeHeader()` method was never documented as an officially supported API.

### DEP0064: tls.createSecurePair()#

Type: Runtime

The `tls.createSecurePair()` API was deprecated in documentation in Node.js 0.11.3. Users should use `tls.Socket` instead.

### DEP0065: repl.REPL_MODE_MAGIC and NODE_REPL_MODE=magic#

Type: End-of-Life

The `repl` module's `REPL_MODE_MAGIC` constant, used for `replMode` option, has been removed. Its behavior has been functionally identical to that of `REPL_MODE_SLOPPY` since Node.js 6.0.0, when V8 5.0 was imported. Please use `REPL_MODE_SLOPPY` instead.

The `NODE_REPL_MODE` environment variable is used to set the underlying `replMode` of an interactive `node` session. Its value, `magic`, is also removed. Please use `sloppy` instead.

### DEP0066: outgoingMessage._headers, outgoingMessage._headerNames#

Type: Documentation-only

The `http` module `outgoingMessage._headers` and `outgoingMessage._headerNames` properties have been deprecated. Please instead use one of the public methods (e.g. `outgoingMessage.getHeader()`, `outgoingMessage.getHeaders()`, `outgoingMessage.getHeaderNames()`, `outgoingMessage.hasHeader()`, `outgoingMessage.removeHeader()`, `outgoingMessage.setHeader()`) for working with outgoing headers.

The `outgoingMessage._headers` and `outgoingMessage._headerNames` properties were never documented as officially supported properties.

### DEP0067: OutgoingMessage.prototype._renderHeaders#

Type: Documentation-only

The `http` module `OutgoingMessage.prototype._renderHeaders()` API has been deprecated.

The `OutgoingMessage.prototype._renderHeaders` property was never documented as an officially supported API.

### DEP0068: node debug#

Type: Runtime

`node debug` corresponds to the legacy CLI debugger which has been replaced with a V8-inspector based CLI debugger available through `node inspect`.

### DEP0069: vm.runInDebugContext(string)#

Type: End-of-Life

DebugContext has been removed in V8 and is not available in Node.js 10+.

DebugContext was an experimental API.

### DEP0070: async_hooks.currentId()#

Type: End-of-Life

`async_hooks.currentId()` was renamed to `async_hooks.executionAsyncId()` for clarity.

This change was made while `async_hooks` was an experimental API.

### DEP0071: async_hooks.triggerId()#

Type: End-of-Life

`async_hooks.triggerId()` was renamed to `async_hooks.triggerAsyncId()` for clarity.

This change was made while `async_hooks` was an experimental API.

### DEP0072: async_hooks.AsyncResource.triggerId()#

Type: End-of-Life

`async_hooks.AsyncResource.triggerId()` was renamed to `async_hooks.AsyncResource.triggerAsyncId()` for clarity.

This change was made while `async_hooks` was an experimental API.

### DEP0073: Several internal properties of net.Server#

Type: End-of-Life

Accessing several internal, undocumented properties of `net.Server` instances with inappropriate names has been deprecated.

As the original API was undocumented and not generally useful for non-internal code, no replacement API is provided.

### DEP0074: REPLServer.bufferedCommand#

Type: Runtime

The `REPLServer.bufferedCommand` property was deprecated in favor of `REPLServer.clearBufferedCommand()`.

### DEP0075: REPLServer.parseREPLKeyword()#

Type: Runtime

`REPLServer.parseREPLKeyword()` was removed from userland visibility.

### DEP0076: tls.parseCertString()#

Type: Runtime

`tls.parseCertString()` is a trivial parsing helper that was made public by mistake. This function can usually be replaced with:

    const querystring = require('querystring');
    querystring.parse(str, '\n', '=');

This function is not completely equivalent to `querystring.parse()`. One difference is that `querystring.parse()` does url decoding:

    > querystring.parse('%E5%A5%BD=1', '\n', '=');
    { '好': '1' }
    > tls.parseCertString('%E5%A5%BD=1');
    { '%E5%A5%BD': '1' }

### DEP0077: Module._debug()#

Type: Runtime

`Module._debug()` has been deprecated.

The `Module._debug()` function was never documented as an officially supported API.

### DEP0078: REPLServer.turnOffEditorMode()#

Type: Runtime

`REPLServer.turnOffEditorMode()` was removed from userland visibility.

### DEP0079: Custom inspection function on Objects via .inspect()#

Type: Runtime

Using a property named `inspect` on an object to specify a custom inspection function for `util.inspect()` is deprecated. Use `util.inspect.custom` instead. For backward compatibility with Node.js prior to version 6.4.0, both may be specified.

### DEP0080: path._makeLong()#

Type: Documentation-only

The internal `path._makeLong()` was not intended for public use. However, userland modules have found it useful. The internal API has been deprecated and replaced with an identical, public `path.toNamespacedPath()` method.

### DEP0081: fs.truncate() using a file descriptor#

Type: Runtime

`fs.truncate()` `fs.truncateSync()` usage with a file descriptor has been deprecated. Please use `fs.ftruncate()` or `fs.ftruncateSync()` to work with file descriptors.

### DEP0082: REPLServer.prototype.memory()#

Type: Runtime

`REPLServer.prototype.memory()` is only necessary for the internal mechanics of the `REPLServer` itself. Do not use this function.

### DEP0083: Disabling ECDH by setting ecdhCurve to false#

Type: Runtime

The `ecdhCurve` option to `tls.createSecureContext()` and `tls.TLSSocket` could be set to `false` to disable ECDH entirely on the server only. This mode is deprecated in preparation for migrating to OpenSSL 1.1.0 and consistency with the client. Use the `ciphers` parameter instead.

### DEP0084: requiring bundled internal dependencies#

Type: Runtime

Since Node.js versions 4.4.0 and 5.2.0, several modules only intended for internal usage are mistakenly exposed to user code through `require()`. These modules are:

- `v8/tools/codemap`
- `v8/tools/consarray`
- `v8/tools/csvparser`
- `v8/tools/logreader`
- `v8/tools/profile_view`
- `v8/tools/profile`
- `v8/tools/SourceMap`
- `v8/tools/splaytree`
- `v8/tools/tickprocessor-driver`
- `v8/tools/tickprocessor`
- `node-inspect/lib/_inspect` (from 7.6.0)
- `node-inspect/lib/internal/inspect_client` (from 7.6.0)
- `node-inspect/lib/internal/inspect_repl` (from 7.6.0)

The `v8/*` modules do not have any exports, and if not imported in a specific order would in fact throw errors. As such there are virtually no legitimate use cases for importing them through `require()`.

On the other hand, `node-inspect` may be installed locally through a package manager, as it is published on the npm registry under the same name. No source code modification is necessary if that is done.

### DEP0085: AsyncHooks Sensitive API#

Type: End-of-Life

The AsyncHooks Sensitive API was never documented and had various minor issues. (See https://github.com/nodejs/node/issues/15572.) Use the `AsyncResource` API instead.

### DEP0086: Remove runInAsyncIdScope#

Type: End-of-Life

`runInAsyncIdScope` doesn't emit the `'before'` or `'after'` event and can thus cause a lot of issues. See https://github.com/nodejs/node/issues/14328 for more details.

### DEP0089: require('assert')#

Type: Documentation-only

Importing assert directly is not recommended as the exposed functions will use loose equality checks. Use `require('assert').strict` instead. The API is the same as the legacy assert but it will always use strict equality checks.

### DEP0090: Invalid GCM authentication tag lengths#

Type: Runtime

Node.js supports all GCM authentication tag lengths which are accepted by OpenSSL when calling `decipher.setAuthTag()`. This behavior will change in a future version at which point only authentication tag lengths of 128, 120, 112, 104, 96, 64, and 32 bits will be allowed. Authentication tags whose length is not included in this list will be considered invalid in compliance with NIST SP 800-38D.

### DEP0091: crypto.DEFAULT_ENCODING#

Type: Runtime

The `crypto.DEFAULT_ENCODING` property is deprecated.

### DEP0092: Top-level `this` bound to `module.exports`#

Type: Documentation-only

Assigning properties to the top-level `this` as an alternative to `module.exports` is deprecated. Developers should use `exports` or `module.exports` instead.

### DEP0093: crypto.fips is deprecated and replaced.#

Type: Documentation-only

The `crypto.fips` property is deprecated. Please use `crypto.setFips()` and `crypto.getFips()` instead.

### DEP0094: Using `assert.fail()` with more than one argument.#

Type: Runtime

Using `assert.fail()` with more than one argument is deprecated. Use `assert.fail()` with only one argument or use a different `assert` module method.

### DEP0095: timers.enroll()#

Type: Runtime

`timers.enroll()` is deprecated. Please use the publicly documented `setTimeout()` or `setInterval()` instead.

### DEP0096: timers.unenroll()#

Type: Runtime

`timers.unenroll()` is deprecated. Please use the publicly documented `clearTimeout()` or `clearInterval()` instead.

### DEP0097: MakeCallback with domain property#

Type: Runtime

Users of `MakeCallback` that add the `domain` property to carry context, should start using the `async_context` variant of `MakeCallback` or `CallbackScope`, or the high-level `AsyncResource` class.

### DEP0098: AsyncHooks Embedder AsyncResource.emitBefore and AsyncResource.emitAfter APIs#

Type: Runtime

The embedded API provided by AsyncHooks exposes `.emitBefore()` and `.emitAfter()` methods which are very easy to use incorrectly which can lead to unrecoverable errors.

Use `asyncResource.runInAsyncScope()` API instead which provides a much safer, and more convenient, alternative. See https://github.com/nodejs/node/pull/18513 for more details.

### DEP0099: async context-unaware node::MakeCallback C++ APIs#

Type: Compile-time

Certain versions of `node::MakeCallback` APIs available to native modules are deprecated. Please use the versions of the API that accept an `async_context` parameter.

### DEP0100: process.assert()#

Type: Runtime

`process.assert()` is deprecated. Please use the `assert` module instead.

This was never a documented feature.

### DEP0101: --with-lttng#

Type: End-of-Life

The `--with-lttng` compile-time option has been removed.

### DEP0102: Using `noAssert` in Buffer#(read|write) operations.#

Type: End-of-Life

Using the `noAssert` argument has no functionality anymore. All input is going to be verified, no matter if it is set to true or not. Skipping the verification could lead to hard to find errors and crashes.

### DEP0103: process.binding('util').is[...] typechecks#

Type: Documentation-only (supports `--pending-deprecation`)

Using `process.binding()` in general should be avoided. The type checking methods in particular can be replaced by using `util.types`.

### DEP0104: process.env string coercion#

Type: Documentation-only (supports `--pending-deprecation`)

When assigning a non-string property to `process.env`, the assigned value is implicitly converted to a string. This behavior is deprecated if the assigned value is not a string, boolean, or number. In the future, such assignment may result in a thrown error. Please convert the property to a string before assigning it to `process.env`.

### DEP0105: decipher.finaltol#

Type: Runtime

`decipher.finaltol()` has never been documented and is currently an alias for `decipher.final()`. In the future, this API will likely be removed, and it is recommended to use `decipher.final()` instead.

### DEP0106: crypto.createCipher and crypto.createDecipher#

Type: Documentation-only

Using `crypto.createCipher()` and `crypto.createDecipher()` should be avoided as they use a weak key derivation function (MD5 with no salt) and static initialization vectors. It is recommended to derive a key using `crypto.pbkdf2()` and to use `crypto.createCipheriv()` and `crypto.createDecipheriv()` to obtain the `Cipher` and `Decipher` objects respectively.

### DEP0107: tls.convertNPNProtocols()#

Type: Runtime

This was an undocumented helper function not intended for use outside Node.js core and obsoleted by the removal of NPN (Next Protocol Negotiation) support.

### DEP0108: zlib.bytesRead#

Type: Documentation-only

Deprecated alias for `zlib.bytesWritten`. This original name was chosen because it also made sense to interpret the value as the number of bytes read by the engine, but is inconsistent with other streams in Node.js that expose values under these names.