Javascript Array loop traversal of foreach

Last Update:2018-07-19 Source: Internet

Author: User

Tags javascript array

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1. js Array loop traversal. array loop variable, the first thing to think about is the for (Var i=0;i<count;i++) way.

In addition, you can use a simpler foreach method

2. The ForEach function.
Both Firefox and Chrome's array types have foreach functions. Use the following:

<!--Add by oscar999-->
<! DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 transitional//en" >
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<meta name= "Author" content= "oscar999" >
</HEAD>

<BODY>
<script>
var arryall = [];
Arryall.push (1);
Arryall.push (2);
Arryall.push (3);
Arryall.push (4);

Arryall.foreach (function (e) {
	alert (e);
})

</script>
</BODY>
</HTML>

But above, the code does not work correctly in IE.

Because IE's array does not have this method

alert (Array.prototype.forEach);

The execution of the above sentence is "undefined", which means that the Array in IE does not have a foreach method.

3. Make IE compatible with foreach method
Since IE's array does not have a foreach method, we will manually add this prototype method to it.

Array.foreach implementation for IE support.
Https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/forEach
if (! Array.prototype.forEach) {
	Array.prototype.forEach = function (callback, thisarg) {
		var T, K;
		if (this = = null) {
			throw new TypeError ("This is null or not defined");
		}
		var O = Object (this);
		var len = o.length >>> 0; Hack to convert O.length to a UInt32
		if ({}.tostring.call (callback)!= "[Object Function]") {
			throw new Typee Rror (callback + "is not a function");
		}
		if (thisarg) {
			T = Thisarg;
		}
		k = 0;
		while (K < Len) {
			var kvalue;
			if (k in O) {
				kvalue = o[k];
				Callback.call (T, Kvalue, K, O);
			}
			k++;}}

Detailed introduction can refer to:
Https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/forEach

4. How to jump out of the loop.
Js This kind of condition foreach cannot use continue, break; You can use the following two ways:
1. If statement control
2. Return. (return True, false)
Return--> similar to continue

The following example is the number of multiples of 2 in an array and a multiple of 3;

<!--Add by oscar999--> <! DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 transitional//en" > <HTML> <HEAD> <TITLE> New Document </ title> <meta name= "Author" content= "oscar999" > </HEAD> <BODY> <script> if (!
		Array.prototype.forEach) {Array.prototype.forEach = function (callback, thisarg) {var T, K;
		if (this = = null) {throw new TypeError ("This is null or not defined");
		var O = Object (this); var len = o.length >>> 0; Hack to convert O.length to a UInt32 if ({}.tostring.call (callback)!= "[Object Function]") {throw new TypeError (
		Callback + "is not a function");
		} if (thisarg) {T = Thisarg;
		} k = 0;
			while (K < Len) {var kvalue;
				if (k in O) {kvalue = o[k];
			Callback.call (T, Kvalue, K, O);
		} k++;
}
	};
} var arryall = [];
Arryall.push (1);
Arryall.push (2);
Arryall.push (3);
Arryall.push (4);

Arryall.push (5);

var arryspecial = []; Arryall.foreach (function (e) {if (e)%2==0) {Arryspecial.push (e);
	}else if (e%3==0) {Arryspecial.push (e);
 }) </script> </BODY> </HTML>

Use return to achieve the above effect

Arryall.foreach (function (e) {
	if (e%2==0)
    {
		arryspecial.push (e);
		return;
	}
	if (e%3==0)
    {    
		arryspecial.push (e);
		return;
	}
})

As for how to write the effect of similar break, there is no better way to find out.

There is a search, some say return false can be reached, tried, the effect and return and return ture is the same.

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