javascript--face question

(1) How does JavaScript empty an array?

Such as

var arrayList = [' A ', ' B ', ' C ', ' d ', ' e ', ' F '];

How to EmptyarrayList

Method 1: Directly change the object that the ArrayList points to, the original object does not change.

ArrayList = [];

Method 2: This method clears the original array by setting the length=0 element.

arraylist.length = 0;

Method 3

Arraylist.splice (0, arraylist.length);

(2) How can I tell if an object is an array? Method 1: Use Object.prototype.toString to determine if it is an array, and call is used here to point the this in toString to obj. And then complete judgment.

function IsArray (obj) {    return Object.prototype.toString.call (obj) = = = ' [Object Array] ';}

Method Two: Using the prototype chain to complete the judgment, the basic idea is to use an instance if it is constructed by a constructor, then its __proto__is a pointer to the constructor prototypeProperty.

function IsArray (obj) {    return obj.__proto__ = = = Array.prototype;}

Method 3: Use jquery

function IsArray (obj) {    return  $.isarray (obj)}

javascript--face question