Node.js util 模块

继承

JavaScript

const util = require('node:util');
const { EventEmitter } = require('node:events');

// 老写法（ES5）
function Old() {
  EventEmitter.call(this);
}
util.inherits(Old, EventEmitter);

// 新写法（ES6+，推荐）
class New extends EventEmitter {}

const n = new New();
n.on('x', (v) => console.log('收到', v));
n.emit('x', 1);

Output

收到 1

类型判断

JavaScript

const { types } = require('node:util');

const checks = [
  ['isPromise', Promise.resolve()],
  ['isDate', new Date()],
  ['isRegExp', /x/],
  ['isMap', new Map()],
  ['isTypedArray', new Uint8Array(4)],
  ['isProxy', new Proxy({}, {})],
];

for (const [fn, val] of checks) {
  console.log(fn, types[fn](val));
}

Output

isPromise true
isDate true
isRegExp true
isMap true
isTypedArray true
isProxy true

util.types reads V8 internal type tags, so it beats instanceof and typeof — especially across vm contexts and worker_threads.

调试输出

JavaScript

const util = require('node:util');
const debug = util.debuglog('db');

debug('连接 %s', 'mysql://localhost');   // 默认不输出

Bash

NODE_DEBUG=db node app.js

Output

DB 24188: 连接 mysql://localhost

debuglog is a zero-dependency conditional logger: silent by default, enabled by an env var. Cleaner than sprinkling if (DEBUG).

废弃警告

JavaScript

const util = require('node:util');

const oldApi = util.deprecate(
  (x) => x * 2,
  'oldApi 将在 v3 移除，请改用 newApi',
  'DEP0001'
);

oldApi(2);   // 正常返回值，但打印一条 DeprecationWarning

Output

(node:24188) DeprecationWarning: oldApi 将在 v3 移除，请改用 newApi
(Use `node --trace-deprecation ...` to show where the warning was created)

其他常用

API	Use
`util.format`	printf 风格格式化
`util.inspect`	把对象转成可读字符串
`util.isDeepStrictEqual`	严格深比较
`util.parseArgs`	解析命令行参数
`util.aborted`	把 signal 转成 Promise
`util.stripVTControlCharacters`	去掉终端颜色码

JavaScript

const util = require('node:util');

const ac = new AbortController();
setTimeout(() => ac.abort(), 100);

await util.aborted(ac.signal);
console.log('已中止');

Output

已中止

继承

JavaScript

const util = require('node:util');
const { EventEmitter } = require('node:events');

// 老写法（ES5）
function Old() {
  EventEmitter.call(this);
}
util.inherits(Old, EventEmitter);

// 新写法（ES6+，推荐）
class New extends EventEmitter {}

const n = new New();
n.on('x', (v) => console.log('收到', v));
n.emit('x', 1);

Output

收到 1

类型判断

JavaScript

const { types } = require('node:util');

const checks = [
  ['isPromise', Promise.resolve()],
  ['isDate', new Date()],
  ['isRegExp', /x/],
  ['isMap', new Map()],
  ['isTypedArray', new Uint8Array(4)],
  ['isProxy', new Proxy({}, {})],
];

for (const [fn, val] of checks) {
  console.log(fn, types[fn](val));
}

Output

isPromise true
isDate true
isRegExp true
isMap true
isTypedArray true
isProxy true

util.types 用的是 V8 内部类型标记，比 instanceof 和 typeof 都准，尤其在跨 vm 上下文和 worker_threads 时。

调试输出

JavaScript

const util = require('node:util');
const debug = util.debuglog('db');

debug('连接 %s', 'mysql://localhost');   // 默认不输出

Bash

NODE_DEBUG=db node app.js

Output

DB 24188: 连接 mysql://localhost

debuglog 是零依赖的条件日志：平时完全静默，需要时用环境变量打开。比到处 if (DEBUG) 干净。

废弃警告

JavaScript

const util = require('node:util');

const oldApi = util.deprecate(
  (x) => x * 2,
  'oldApi 将在 v3 移除，请改用 newApi',
  'DEP0001'
);

oldApi(2);   // 正常返回值，但打印一条 DeprecationWarning

Output

(node:24188) DeprecationWarning: oldApi 将在 v3 移除，请改用 newApi
(Use `node --trace-deprecation ...` to show where the warning was created)

其他常用

API	用途
`util.format`	printf 风格格式化
`util.inspect`	把对象转成可读字符串
`util.isDeepStrictEqual`	严格深比较
`util.parseArgs`	解析命令行参数
`util.aborted`	把 signal 转成 Promise
`util.stripVTControlCharacters`	去掉终端颜色码

JavaScript

const util = require('node:util');

const ac = new AbortController();
setTimeout(() => ac.abort(), 100);

await util.aborted(ac.signal);
console.log('已中止');

Output

已中止

Node.js util 模块

继承

类型判断

调试输出

废弃警告

其他常用

继承

类型判断

调试输出

废弃警告

其他常用

Friends & Partners