jQuery兼容浏览器IE8方法

1.前言

　　在做前端开发的时候，公司的规范要求面向客户的兼容到IE8，但是在IE8模式下经常会发现各种错误，某某方法未定义、不支持某属性或对象等，使用jQuery的时候，jQuery从2.0开始不兼容IE8，最低支持IE9，所以需要引入更低的jQuery版本来兼容。

2.IE8不支持jQuery版本解决办法

通过判断IE浏览器的版本来加载对应版本的jQuery

使用语句 可在IE8模式下进行一些兼容操作。代码如下：

1 <script type="text/javascript" src="<%=path%>/js/jquery-3.1.1.min.js"></script>
2 <!--[if IE 8]>
3 <script type="text/javascript" src="<%=path%>/js/jquery-1.9.1.min.js"></script>
4 <![endif]-->

　　这样在切换到IE8时，低版本的jQuery就会覆盖高版本的jQuery。如果在IE8下需要调整某些元素的样式的话，最好将JS代码放在页面底部（并注意是否有行内样式），不然为某些动态加载的内容设置的样式可能不会生效。

3.IE8不支持forEach解决办法

为不支持forEach的浏览器添加自定义forEach方法

　　代码如下：

1 if (typeof Array.prototype.forEach != 'function') {
2     Array.prototype.forEach = function (callback) {
3         for (var i = 0; i < this.length; i++) {
4             callback.apply(this, [this[i], i, this]);
5         }
6     };
7 }

如果是引入的jQuery插件，可将该段代码放在插件内容的开头即可，这样在IE8下执行forEach方法就不会报错了。

4.IE8不支持map解决办法

添加自定义forEach方法

 1 if (!Array.prototype.map) {
 2     Array.prototype.map = function(callback, thisArg) {
 3         var T, A, k;
 4         if (this == null) {
 5             throw new TypeError(" this is null or not defined");
 6         }
 7         // 1. Let O be the result of calling ToObject passing the |this| value as the argument.
 8         var O = Object(this);
 9         // 2. Let lenValue be the result of calling the Get internal method of O with the argument "length".
10         // 3. Let len be ToUint32(lenValue).
11         var len = O.length >>> 0;
12         // 4. If IsCallable(callback) is false, throw a TypeError exception.
13         // See: http://es5.github.com/#x9.11
14         if (typeof callback !== "function") {
15             throw new TypeError(callback + " is not a function");
16         }
17         // 5. If thisArg was supplied, let T be thisArg; else let T be undefined.
18         if (thisArg) {
19             T = thisArg;
20         }
21         // 6. Let A be a new array created as if by the expression new Array(len) where Array is
22         // the standard built-in constructor with that name and len is the value of len.
23         A = new Array(len);
24         // 7. Let k be 0
25         k = 0;
26         // 8. Repeat, while k < len
27         while(k < len) {
28             var kValue, mappedValue;
29             // a. Let Pk be ToString(k).
30             //   This is implicit for LHS operands of the in operator
31             // b. Let kPresent be the result of calling the HasProperty internal method of O with argument Pk.
32             //   This step can be combined with c
33             // c. If kPresent is true, then
34             if (k in O) {
35                 // i. Let kValue be the result of calling the Get internal method of O with argument Pk.
36                 kValue = O[ k ];
37                 // ii. Let mappedValue be the result of calling the Call internal method of callback
38                 // with T as the this value and argument list containing kValue, k, and O.
39                 mappedValue = callback.call(T, kValue, k, O);
40                 // iii. Call the DefineOwnProperty internal method of A with arguments
41                 // Pk, Property Descriptor {Value: mappedValue, : true, Enumerable: true, Configurable: true},
42                 // and false.
43                 // In browsers that support Object.defineProperty, use the following:
44                 // Object.defineProperty(A, Pk, { value: mappedValue, writable: true, enumerable: true, configurable: true });
45                 // For best browser support, use the following:
46                 A[ k ] = mappedValue;
47             }
48             // d. Increase k by 1.
49             k++;
50         }
51         // 9. return A
52         return A;
53     };
54 }