25_underscore.js_isarraylike.html

<meta charset= "Utf-8" ><p></p><p></p><p></p><p></p><p ></p><style>*{margin:0;padding:0;} Pre{padding:10px;display:block;background-color: #eee; color:blue;font-size:20px;} </style><pre><!--today, let's explore how to make judgments an object is a class array object-->//we also need to use the last var shallowproperty = function (key) { return function (obj) {return obj = = null? void 0:obj[key];}; }; First we have to figure out what the class array is to var arr = array ();//This is the real array with the Length property Console.log (arr.length)//0// A real array object is one that can use all the methods on the Array.prototype object//But the class array also has the Length property//But they can't use all the methods on the Array.prototype//That's where the difference is. var o = {length: 2, Name: ' Ken ', age:18}//Then those are Class array objects///such as arguments in function parameters//such as DOM objects, we get through the getelementsby* and other methods of collection are class array//can use subscript operation,/ /But how can we tell if an object is a class array object//The light judging with the length attribute is not feasible,//above we said that they do not have all the methods on the Array.prototype//The value of the length property must be limited//below we come to see our und How is erscore.js implemented? var Max_array_index = Math.pow (2, 53)-1; var getlength = shallowproperty (' length '); var Isarraylike = function (collection) {//Gets the length property var length = GetLength (collection);//Determines whether the type of length is number type return typeof Lengt h = = ' number ' && length >= 0 && length <= max_array_index;}; Console.log (Isarraylike (o))//But we don't feel accurate enough.//I think we should judge the method//ourselves to implement the following var isarraylike = function (collection) {var length = GetLength (collection); Return (! ( Array.prototype.alice in collection) &&! (Array.prototype.split in collection)) && typeof length = = = ' Number ' && length>=0 && length<=max_array_index;} var oPs = Document.queryselectorall ("P") Console.log (Isarraylike (o));//trueconsole.log (Isarraylike (oPs));// Truefunction Call (A, b) {Console.log (isarraylike (arguments));//true;} Call (</pre>#), attach my github address here