Comments (1)
typeof操作符
js中检测数据类型的一种方式,可轻松检测出常用类型,例如,String,Number,Boolean,Function,Undefind,但在对象和数组之间它分不清除。
let a=[];
let b={};
console.log(typeof(a)); //object
console.log(typeof(b));//object
console.log(typeof(null));//object
instanceof操作符
instanceof操作符用于测试一个对象在其原型链中是否存一个构造函数的prototype属性。
eg. Object instanceof constructor
object:要检测的对象
constructor:某个构造函数
console.log({} instanceof Array); // fasle
console.log([] instanceof Array); // true
console.log({} instanceof Object); // true
console.log([] instanceof Object); // true
Array、Function的原型都是Object
通过constructor来判断
如果是数组,那么arr.constructor === Array(不准确,因为我们可以指定obj.constructor = Array)
let a = 1;
console.log(a.constructor === Array); // false
a.constructor = Array;
console.log(a.constructor === Array); // true
使用Object.prototype.toString.call判断
如果值是[object Array],说明是数组
console.log(Object.prototype.toString.call([])); // [object Array]
console.log(Object.prototype.toString.call({})); // [object Object]
Array.prototype.isPrototypeOf
console.log(Array.prototype.isPrototypeOf([])); // true
console.log(Array.prototype.isPrototypeOf({})); // false
console.log(Object.prototype.isPrototypeOf([])); // true
console.log(Object.prototype.isPrototypeOf({})); // true
Array、Function的原型都是Object
Array.isArray()
let a = [];
Array.isArray(); // true
能判断数组的方法有:Object instanceof constructor,Object.prototype.toString.call, Array.prototype.isPrototypeOf,Array.isArray()
能区分数组和对象的方法 Object.prototype.toString.call,Array.isArray()
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