jQuery兼容瀏覽器IE8方法

1.前言

　　在做前端開發的時候，公司的規范要求面向客戶的兼容到IE8，但是在IE8模式下經常會發現各種錯誤，某某方法未定義、不支持某屬性或對象等，使用jQuery的時候，jQuery從2.0開始不兼容IE8，最低支持IE9，所以需要引入更低的jQuery版本來兼容。

2.IE8不支持jQuery版本解決辦法

• 通過判斷IE瀏覽器的版本來加載對應版本的jQuery

　　使用語句<!--[if IE 8]> 僅IE8可識別 <![endif]--> 可在IE8模式下進行一些兼容操作。代碼如下：

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

　　這樣在切換到IE8時，低版本的jQuery就會覆蓋高版本的jQuery。如果在IE8下需要調整某些元素的樣式的話，最好將JS代碼放在頁面底部（並注意是否有行內樣式），不然為某些動態加載的內容設置的樣式可能不會生效。

3.IE8不支持forEach解決辦法

• 為不支持forEach的瀏覽器添加自定義forEach方法

　　代碼如下：

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，可將該段代碼放在插件內容的開頭即可，這樣在IE8下執行forEach方法就不會報錯了。 

 4.IE8不支持map解決辦法

• 添加自定義forEach方法

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.
        var O = Object(this);  9         // 2. Let lenValue be the result of calling the Get internal method of O with the argument "length".
        // 3. Let len be ToUint32(lenValue).
        var len = O.length >>> 0; 12         // 4. If IsCallable(callback) is false, throw a TypeError exception.
        // See: http://es5.github.com/#x9.11
        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.
        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
        // the standard built-in constructor with that name and len is the value of len.
        A = new Array(len); 24         // 7. Let k be 0
        k = 0; 26         // 8. Repeat, while k < len
        while(k < len) { 28             var kValue, mappedValue; 29             // a. Let Pk be ToString(k).
            // This is implicit for LHS operands of the in operator
            // b. Let kPresent be the result of calling the HasProperty internal method of O with argument Pk.
            // This step can be combined with c
            // c. If kPresent is true, then
            if (k in O) { 35                 // i. Let kValue be the result of calling the Get internal method of O with argument Pk.
                kValue = O[ k ]; 37                 // ii. Let mappedValue be the result of calling the Call internal method of callback
                // with T as the this value and argument list containing kValue, k, and O.
                mappedValue = callback.call(T, kValue, k, O); 40                 // iii. Call the DefineOwnProperty internal method of A with arguments
                // Pk, Property Descriptor {Value: mappedValue, : true, Enumerable: true, Configurable: true},
                // and false.
                // In browsers that support Object.defineProperty, use the following:
                // Object.defineProperty(A, Pk, { value: mappedValue, writable: true, enumerable: true, configurable: true });
                // For best browser support, use the following:
                A[ k ] = mappedValue; 47  } 48             // d. Increase k by 1.
            k++; 50  } 51         // 9. return A
        return A; 53  }; 54 }