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浅谈JS判断类型的几个方法

news 来源：原创 2025/5/10 9:46:36

1. typeof

只能判断基本数据类型(null除外)，对应复杂类型如数组，对象判断不了，均返回Object

console.log(typeof '123')  // string

console.log(typeof 123) // number

console.log(typeof true) // boolean

console.log(typeof false) // boolean

console.log(typeof null) // object

console.log(typeof undefined) // undefined

console.log(typeof Symbol('123')) // symbol

console.log(typeof {}) // object

console.log(typeof []) // object

console.log(typeof function(){}) // function

console.log(typeof new Date()) // object

console.log(typeof  /abc/) // object

2. instanceof

instanceof 可以判断数组和对象，但是后面要跟Array才能判断，但对于基本类型一律返回false

console.log('123' instanceof String)  // false
console.log(null instanceof Object)  // false
console.log( {} instanceof Array) // false
console.log( [] instanceof Array) // true
console.log( {} instanceof Object) // true
console.log( ['a'] instanceof Object) // true
console.log( function(){} instanceof Function) // true
console.log (function(){}  instanceof Object) // true
console.log ((new Date()) instanceof Object) // true
console.log ((new Date()) instanceof Date) // true

3. Array.isArray()

Array.isArray()判断类型是否为数组

console.log(Array.isArray([])) // true
console.log(Array.isArray({})) // false
console.log(Array.isArray('abc')) // false
console.log(Array.isArray(null)) // false
console.log(Array.isArray(undefined)) // false
console.log(Array.isArray(function(){})) // false

4. contructor属性

判断null和undefined时候报错

console.log('123'.constructor === Number) // false
console.log((123).constructor === Number) // true
console.log([].constructor === Array) // true
console.log({}.constructor === Array) // false
console.log([].constructor === Object) // false
console.log({}.constructor === Object) // true
console.log(/abc/.constructor === Object) // false
console.log(/abc/.constructor === RegExp) // true
console.log(null.constructor)  // 报错
console.log(undefined.constructor) // 报错

5.Object.prototype.toString.call()

推荐

console.log(Object.prototype.toString.call(123)) // [object Number]
console.log(Object.prototype.toString.call('123')) // [object String]
console.log(Object.prototype.toString.call(true)) // [object Boolean]
console.log(Object.prototype.toString.call(null)) // [object Null]
console.log(Object.prototype.toString.call(undefined)) // [object Undefined]
console.log(Object.prototype.toString.call(Symbol('123'))) // [object Symbol]
console.log(Object.prototype.toString.call({})) // [object Object]
console.log(Object.prototype.toString.call([])) // [object Array]
console.log(Object.prototype.toString.call(() => {})) // [object Function]
console.log(Object.prototype.toString.call(new Date())) // [object Date]
console.log(Object.prototype.toString.call(new RegExp())) // [object RegExp]
console.log(Object.prototype.toString.call(new Error())) // [object Error]
console.log(Object.prototype.toString.call(new Map())) // [object Map]
console.log(Object.prototype.toString.call(new Set())) // [object Set]