Module util

The util module provides practical tool functions such as judgment of data type, copying of object attributes, parsing of template strings, and event processing.

The following is a specific introduction and examples:

Determine the data type - util.is[type] This module provides methods such as isDate, isRegExp, isErroretc. to determine the data type of the incoming parameters, for example:

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var util = require('util');
console.log(util.isDate(new Date()));
console.log(util.isRegExp(/some regexp/));

Object property copying - util.inherits() This method can optionally inherit one constructor from another, thus implementing prototypal inheritance.

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var util = require('util');

function Animal() {
    this.name = 'Animal';
    this.sleep = function() {
        console.log(this.name + '正在睡觉！');
    }
}
Animal.prototype.eat = function(food) {
    console.log(this.name + '正在吃：' + food);
};

function Cat() {
    this.name = 'cat';
}
util.inherits(Cat, Animal);

Use Catthis constructor to inherit Animalthe instance properties and prototype properties of , and print Catthe properties and methods of the instance.

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var cat = new Cat();
console.log(cat.name);
console.log(cat.eat('fish'));
console.log(cat.sleep());

util.format() Formatted output template

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const util = require('util');
const str1 = util.format('%s:%s', 'foo');
const str2 = util.format('%s:%s', 'foo', 'bar', 'baz');
console.log(str1) // => 'foo:%s'
console.log(str2) // => 'foo:bar baz'

The above are utilsome common methods of modules, which can often be used to simplify the actual development process.

object

LruCache

LRU (least recently used) cache object, seeLruCacheobject.

1LruCache util.LruCache;

TextDecoder

TextDecoderdecoding object, seeTextDecoderobject.

1TextDecoder util.TextDecoder;

TextEncoder

TextEncoderEncoding objects, seeTextEncoderobject.

1TextEncoder util.TextEncoder;

types

typesThe module provides tool functions for determining data types.

1types util.types;

static function

format

Format variables according to the specified format

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static String util.format(String fmt,
    ...args);

Call parameters:

fmt: String, format string
args: ..., optional parameter list

Return results:

String, returns the formatted string

format format variable

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static String util.format(...args);

Call parameters:

args: ..., optional parameter list

Return results:

String, returns the formatted string

inherits

Inherit prototype functions from one constructor to another. The prototype of the constructor will be set to a new object created from the superclass (superConstructor).

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static util.inherits(Value constructor,
    Value superConstructor);

Call parameters:

constructor: Value, initial constructor
superConstructor: Value, the inherited super class

inspect

The function returns the string representation of obj, mainly used for debugging. Additional options can be used to change certain aspects of the formatted string.

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static String util.inspect(Value obj,
    Object options = {});

Call parameters:

obj: Value, specifies the object to be processed
options: Object, specify format control options

Return results:

String, returns the formatted string

The following parameters are supported:

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9{
    "colors": false, // specify if output should be colorized, defaults to false
    "depth": 2, // specify the max depth of the output, defaults to 2
    "table": false, // specify if output should be a table, defaults to false
    "encode_string": true, // specify if string should be encoded, defaults to true
    "maxArrayLength": 100, // specify max number of array elements to show, set to 0 or negative to show no elements, defaults to 100
    "maxStringLength": 10000, // specify max string length to output, set to 0 or negative to show no strings, defaults to 10000
    "fields": [], // specify the fields to be displayed, defaults to all
}

deprecate

Encapsulates the given function. This function is only compatible and does not output warnings.

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static Function util.deprecate(Function fn,
    String msg,
    String code = "");

Call parameters:

fn: Function, given the function that needs to be encapsulated
msg: String, given warning message
code: String, given warning number

Return results:

Function, if the encapsulation result

isEmpty

Checks if the given variable contains no value (no enumerable properties)

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static Boolean util.isEmpty(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, returns True if empty

isArray

Checks whether the given variable is an array

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static Boolean util.isArray(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, returns True if it is an array

isBoolean

Tests whether the given variable is a Boolean

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static Boolean util.isBoolean(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, if it is Boolean, it returns True

isNull

Checks whether the given variable is Null

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static Boolean util.isNull(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, if it is Null, it returns True

isNullOrUndefined

Checks whether the given variable is Null or Undefined

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static Boolean util.isNullOrUndefined(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, if it is Null or Undefined, it returns True

isNumber

Tests whether the given variable is a number

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static Boolean util.isNumber(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, returns True if it is a number

isBigInt

Tests whether the given variable is a BigInt

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static Boolean util.isBigInt(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, returns True if it is a number

isString

Checks whether the given variable is a string

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static Boolean util.isString(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, returns True if it is a string

isUndefined

Checks whether the given variable is Undefined

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static Boolean util.isUndefined(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, if it is Undefined, return True

isRegExp

Tests whether the given variable is a regular object

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static Boolean util.isRegExp(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, returns True if it is a regular object

isObject

Tests whether the given variable is an object

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static Boolean util.isObject(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, returns True if it is an object

isDate

Tests whether the given variable is a date object

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static Boolean util.isDate(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, returns True if it is a date object

isNativeError

Tests whether the given variable is an error object

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static Boolean util.isNativeError(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, returns True if it is an error object

isPrimitive

Checks whether the given variable is of primitive type

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static Boolean util.isPrimitive(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, returns True if it is a primitive type

isSymbol

Check whether the given variable is of type Symbol

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static Boolean util.isSymbol(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, if it is a Symbol type, it returns True

isDataView

Checks whether the given variable is of type DataView

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static Boolean util.isDataView(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, if it is a DataView type, it returns True

isExternal

Checks whether the given variable is of type External

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static Boolean util.isExternal(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, if it is an External type, it returns True

isMap

Check whether the given variable is of type Map

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static Boolean util.isMap(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, if it is a Map type, it returns True

isMapIterator

Checks whether the given variable is of type MapIterator

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static Boolean util.isMapIterator(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, returns True if it is a MapIterator type

isPromise

Checks whether the given variable is of type Promise

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static Boolean util.isPromise(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, if it is a Promise type, it returns True

isAsyncFunction

Checks whether the given variable is of type AsyncFunction

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static Boolean util.isAsyncFunction(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, if it is an AsyncFunction type, it returns True

isSet

Checks whether the given variable is of type Set

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static Boolean util.isSet(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, if it is a Set type, it returns True

isSetIterator

Checks whether the given variable is of type SetIterator

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static Boolean util.isSetIterator(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, if it is a SetIterator type, it returns True

isTypedArray

Checks whether the given variable is of type TypedArray

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static Boolean util.isTypedArray(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, if it is a TypedArray type, it returns True

isUint8Array

Checks whether the given variable is of type Uint8Array

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static Boolean util.isUint8Array(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, returns True if it is Uint8Array type

isFunction

Tests whether the given variable is a function object

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static Boolean util.isFunction(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, returns True if it is a function object

isBuffer

Tests whether the given variable is a functionBufferobject

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static Boolean util.isBuffer(Value v);

Call parameters:

v: Value, given the variable to be detected

Return results:

Boolean, if it is a functionBufferObject returns True

isDeepEqual

Test value depth is equal to expected value

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static Boolean util.isDeepEqual(Value actual,
    Value expected);

Call parameters:

actual: Value, the value to be tested
expected: Value, expected value

Return results:

Boolean, returns True if the depths are equal

has

Query whether the specified object contains the given key

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static Boolean util.has(Value v,
    String key);

Call parameters:

v: Value, given the object to be queried
key: String, specify the key to be queried

Return results:

Boolean, returns an array of all keys of the object

keys

Query all key arrays of the specified object

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static Array util.keys(Value v);

Call parameters:

v: Value, given the object to be queried

Return results:

Array, returns an array of all keys of the object

values

Query all value arrays of the specified object

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static Array util.values(Value v);

Call parameters:

v: Value, given the object to be queried

Return results:

Array, returns an array of all values of the object

clone

Clone the given variable, if it is an object or array, copy the contents to the new object

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static Value util.clone(Value v);

Call parameters:

v: Value, given the variable to be cloned

Return results:

Value, returns the clone result

deepFreeze

Deep freeze an object. The frozen object and the objects it contains will not be allowed to be modified.

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static util.deepFreeze(Value v);

Call parameters:

v: Value, specifies the object to be frozen

extend

Extend the key values of one or more objects to the specified object

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static Value util.extend(Value v,
    ...objs);

Call parameters:

v: Value, specifies the object to be extended
objs: ..., specifies one or more objects for expansion

Return results:

Value, returns the expanded result

_extend

Extend the key values of one or more objects to the specified object, which is an alias of extend

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static Value util._extend(Value v,
    ...objs);

Call parameters:

v: Value, specifies the object to be extended
objs: ..., specifies one or more objects for expansion

Return results:

Value, returns the expanded result

pick

Return aobjectCopy, filter out only the attribute values of the specified key

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static Object util.pick(Value v,
    ...objs);

Call parameters:

v: Value, specifies the object to filter
objs: ..., specify one or more keys for selection

Return results:

Object, returns filtered results

omit

Return aobjectCopy, only excluding the attribute value of the specified key

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static Object util.omit(Value v,
    ...keys);

Call parameters:

v: Value, specifies the object to filter
keys: ..., specify one or more keys for exclusion

Return results:

Object, returns excluded results

first

Get the first element of the array

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static Value util.first(Value v);

Call parameters:

v: Value, given the array to be obtained

Return results:

Value, returns the retrieved element

Get the first multiple elements of an array

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static Value util.first(Value v,
    Integer n);

Call parameters:

v: Value, given the array to be obtained
n: Integer, specifies the number of elements to be obtained

Return results:

Value, returns the obtained array of elements

last

Get the last element of the array

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static Value util.last(Value v);

Call parameters:

v: Value, given the array to be obtained

Return results:

Value, returns the retrieved element

Get multiple elements at the end of an array

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static Value util.last(Value v,
    Integer n);

Call parameters:

v: Value, given the array to be obtained
n: Integer, specifies the number of elements to be obtained

Return results:

Value, returns the obtained array of elements

unique

Get a deduplicated copy of the elements of an array

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static Array util.unique(Value v,
    Boolean sorted = false);

Call parameters:

v: Value, given the array to be duplicated
sorted: Boolean, specifies whether the array is sorted. If the array is sorted, a fast algorithm will be used.

Return results:

Array, returns the array after removing duplicate elements

union

Combine the values of one or more arrays into an array with unique values

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static Array util.union(...arrs);

Call parameters:

arrs: ..., specify one or more arrays for merging

Return results:

Array, returns the merged result

intersection

Returns the intersection of the array containing arr excluding one or more array elements.

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static Array util.intersection(...arrs);

Call parameters:

arrs: ..., specify one or more arrays used to calculate intersection

Return results:

Array, returns the result of calculating the intersection

flatten

Convert an array with multiple levels of nesting (the nesting can be any number of levels) into an array with only one level. If you pass the shallow parameter, the array will be reduced to only one dimension of nesting.

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static Array util.flatten(Value arr,
    Boolean shallow = false);

Call parameters:

arr: Value, specifies the array to be converted
shallow: Boolean, specifies whether to reduce only one dimension of nesting, the default is false

Return results:

Array, returns the result of the conversion

without

Returns an array containing one or more elements in the arr array, excluding one or more elements.

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static Array util.without(Value arr,
    ...els);

Call parameters:

arr: Value, specifies the array to be excluded
els: ..., specifies one or more elements to exclude

Return results:

Array, returns excluded results

difference

Returns an array containing the elements in the arr array excluding the without array elements.

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static Array util.difference(Array list,
    ...arrs);

Call parameters:

list: Array, specifies the array to be excluded
arrs: ..., specifies one or more arrays to exclude

Return results:

Array, returns excluded results

each

Traverse all elements in the list and output each element in order. If the context parameter is passed, the iterator is bound to the context object. Each time iterator is called, three parameters are passed: (element, index, list)

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static Value util.each(Value list,
    Function iterator,
    Value context = undefined);

Call parameters:

list: Value, specifies the list or object to be traversed
iterator: Function, specifies the callback function used for traversal
context: Value, specifies the context object bound when calling the iterator

Return results:

Value, returns the list itself

map

Each value in the list is mapped to a new array through a transformation function (iterator). If the context parameter is passed, the iterator is bound to the context object. Each time iterator is called, three parameters are passed: (element, index, list)

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static Array util.map(Value list,
    Function iterator,
    Value context = undefined);

Call parameters:

list: Value, specifies the list or object to be transformed
iterator: Function, specifies the callback function used for transformation
context: Value, specifies the context object bound when calling the iterator

Return results:

Array, returns the result of the transformation

reduce

Reduce the elements in the list to a single value. If the context parameter is passed, the iterator is bound to the context object. Each time iterator is called, three parameters are passed: (memo, element, index, list)

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static Value util.reduce(Value list,
    Function iterator,
    Value memo,
    Value context = undefined);

Call parameters:

list: Value, specifies the list or object to be summarized
iterator: Function, specifies the callback function used for resolution
memo: Value, specifies the initial value of the reduction
context: Value, specifies the context object bound when calling the iterator

Return results:

Value, returns the summarized result

parseArgs

Parse the command line string and return the parameter list

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static NArray util.parseArgs(String command);

Call parameters:

command: String, specifies the command line string to be parsed

Return results:

NArray, returns the parsed parameter list

compile

Compile script to binary code

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static Buffer util.compile(String srcname,
    String script,
    Integer mode = 0);

Call parameters:

srcname: String, specify the name of the script to be added
script: String, specifies the script code to be compiled
mode: Integer, compilation mode, 0: module, 1: script, 2: worker, default is 0

Return results:

Buffer, returns the compiled binary code

util.compileScripts can be compiled into v8 internal running data blocks (non-machine executable code). The compiled code can be directly loaded and executed by run and require after being saved as *.jsc.

Since after compilation, the target code will not be able to reversely obtain the source code, programs that rely on Function.toString will not run properly.

sync

Wrap callback or async functions to call them synchronously

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static Function util.sync(Function func,
    Boolean async_func = false);

Call parameters:

func: Function, given the function that needs to be wrapped
async_func: Boolean, specifies that func is processed as an async function. If it is false, it will be automatically judged.

Return results:

Function, returns a function that runs synchronously

util.syncProcess the callback function or async function into a sync function to facilitate calling.

The callback example is as follows:

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// callback
var util = require('util');

function cb_test(a, b, cb) {
    setTimeout(() => {
        cb(null, a + b);
    }, 100);
}

var fn_sync = util.sync(cb_test);
console.log(fn_sync(100, 200));

An async example is as follows:

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// async/await
var util = require('util');

async function async_test(a, b) {
    return a + b;
}

var fn_sync = util.sync(async_test);
console.log(fn_sync(100, 200));

For promise-returning functions that are not marked async, sync mode can be specified manually:

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// async/await
var util = require('util');

function async_test(a, b) {
    return new Promise(function(resolve, reject) {
        resolve(a + b);
    });
}

var fn_sync = util.sync(async_test, true);
console.log(fn_sync(100, 200));

promisify

Wrap callback function for async call

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static Function util.promisify(Function func);

Call parameters:

func: Function, given the function that needs to be wrapped

Return results:

Function, returns async function

util.promisifyProcess the callback function as an async function to facilitate calling.

The callback example is as follows:

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// callback
var util = require('util');

function cb_test(a, b, cb) {
    setTimeout(() => {
        cb(null, a + b);
    }, 100);
}

var fn_sync = util.promisify(cb_test);
console.log(async fn_sync(100, 200));

callbackify

Wrap async function for callback call

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static Function util.callbackify(Function func);

Call parameters:

func: Function, given the function that needs to be wrapped

Return results:

Function, return callback function

util.callbackifyProcess the async function into a callback function to facilitate calling.

An async example is as follows:

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// async
var util = require('util');

async function async_test(a, b) {
    return a + b;
}

var fn_callback = util.callbackify(async_test);

fn_callback(100, 200, (err, result) => {
    console.log(result);
});

buildInfo

Query the current engine and component version information

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static Object util.buildInfo();

Return results:

Object, returns the component version object

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24{
    "fibjs": "0.25.0",
    "clang": "9.1",
    "date": "Jun 12 2018 07:22:40",
    "vender": {
        "ev": "4.24",
        "expat": "2.2.5",
        "gd": "2.2.4",
        "jpeg": "8.3",
        "leveldb": "1.17",
        "mongo": "0.7",
        "pcre": "8.21",
        "png": "1.5.4",
        "mbedtls": "2.6.1",
        "snappy": "1.1.2",
        "sqlite": "3.23.0",
        "tiff": "3.9.5",
        "uuid": "1.6.2",
        "v8": "6.7.288.20",
        "v8-snapshot": true,
        "zlib": "1.2.7",
        "zmq": "3.1"
    }
}

Development Guide

Basic module

built-in objects

community module

Module util

object

LruCache

TextDecoder

TextEncoder

types

static function

format

inherits

inspect

deprecate

isEmpty

isArray

isBoolean

isNull

isNullOrUndefined

isNumber

isBigInt

isString

isUndefined

isRegExp

isObject

isDate

isNativeError

isPrimitive

isSymbol

isDataView

isExternal

isMap

isMapIterator

isPromise

isAsyncFunction

isSet

isSetIterator

isTypedArray

isUint8Array

isFunction

isBuffer

isDeepEqual

has

keys

values

clone

deepFreeze

extend

_extend

pick

omit

first

last

unique

union

intersection

flatten

without

difference

each

map

reduce

parseArgs

compile

sync

promisify

callbackify

buildInfo