判断数组的几种方法

instanceof

原型链查找

const arr1 = [1, 2, 3]
const obj = { a: 1 }
console.log(arr1 instanceof Array)  //true
console.log(obj instanceof Array)    //false

Array.isArray()

ES6新方法，用于确定传递的值是否为数组

console.log(Array.isArray([1, 2]))  //true
console.log(Array.isArray({ a: 2 }))    //false

Array.isArray优于instanceof，Array.isArray能检测到iframes，如下

var iframe = document.createElement('iframe')
document.body.appendChild(iframe)
var xArray = window.frames[window.frames.length - 1].Array
var arr = new xArray(1, 2, 3)
console.log(Array.isArray(arr)) //true 
console.log(arr instanceof Array)   //false (不能检测到iframes中的数组)

constructor

 构造函数类型判断

console.log(arr1.constructor === Array)  //true
console.log(obj.constructor === Array)    //false

toString

console.log(Object.prototype.toString.call(arr1) === '[object Array]')  //true
console.log(Object.prototype.toString.call(obj) === '[object Array]')    //false