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js判断类型的方法

爱做梦的老巫婆 2022-04-08 阅读 59
// 1.typeof
console.log(typeof null);//object
console.log(typeof '');//string
console.log(typeof 123);//number
console.log(typeof '123 ');//string
        
// 2.instanceof
var  a = [1,2,3]
console.log(a);//1 2 3
console.log(a instanceof Array); //true
console.log(Array.isArray(a)); //true

let o ={}
console.log(o); //Object
let date = new Date()
console.log(date instanceof Date);//true
let reg = /133/  
console.log(reg instanceof RegExp); //true

function fn(){}
console.log(fn instanceof Function); //true

// 3.toString
console.log(toString.a); //[object Object]
console.log(Object.prototype.toString(a)); //[object Array]
console.log(Object.prototype.toString.call(a)); //[object Array]
console.log(Object.prototype.toString.call(null)); //[object Undefined]

//    4.constructor
console.log(a.constructor == Array); //true
console.log(a.constructor == Object); //false
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