Javascript 陣列迴圈遍歷之forEach(轉載自oscar999)
阿新 • • 發佈:2019-02-04
1. js 陣列迴圈遍歷。
陣列迴圈變數,最先想到的就是 for(var i=0;i<count;i++)這樣的方式了。除此之外,也可以使用較簡便的forEach 方式
2. forEach 函式。
Firefox 和Chrome 的Array 型別都有forEach的函式。使用如下:[html] view plain copy print?
- <!–Add by oscar999–>
- <!DOCTYPE HTML PUBLIC ”-//W3C//DTD HTML 4.0 Transitional//EN”>
- <HTML>
- <HEAD>
- <TITLE
- <METANAME=“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>
<!--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>
但是以上,程式碼在IE中卻無法正常工作。
因為IE的Array 沒有這個方法
- alert(Array.prototype.forEach);
alert(Array.prototype.forEach);
執行以上這句得到的是 “undefined”, 也就是說在IE 中 Array 沒有forEach的方法。
3. 讓IE相容forEach方法
既然IE的Array 沒喲forEach方法, 我們就給它手動新增這個原型方法。[javascript] view plain copy print?
- //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) {
- thrownew 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]”) {
- thrownew 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++;
- }
- };
- }
//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 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++;
}
};
}
詳細介紹可以參照:https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/forEach
4. 如何跳出迴圈?
Js 此種狀況的forEach 不能使用continue, break; 可以使用如下兩種方式:1. if 語句控制
2. return . (return true, false)
return –> 類似continue
以下例子是取出陣列中2的倍數和3的倍數的數;
[html] view plain copy print?
- <!–Add by oscar999–>
- <!DOCTYPE HTML PUBLIC ”-//W3C//DTD HTML 4.0 Transitional//EN”>
- <HTML>
- <HEAD>
- <TITLE> New Document </TITLE>
- <METANAME=“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>
<!--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>
使用return 達到以上效果
[javascript] view plain copy print?
- arryAll.forEach(function(e){
- if(e%2==0)
- {
- arrySpecial.push(e);
- return;
- }
- if(e%3==0)
- {
- arrySpecial.push(e);
- return;
- }
- })
arryAll.forEach(function(e){
if(e%2==0)
{
arrySpecial.push(e);
return;
}
if(e%3==0)
{
arrySpecial.push(e);
return;
}
})
至於如何寫類似break 的效果,目前尚未找到比較好的辦法。
有搜尋一下,有的說return false 可以達成, 試了一下, 效果和return 和return ture 是一樣的。