javascript - IE8 标准不支持array.map 函数？

Question

我没有 IE8，所以我在 IE10 中测试 IE8。当我切换到文档模式的“IE8 标准”时，数组对象的 javascript map 函数给出了一个 javascript 错误：对象不支持属性或方法 'map'

但是当我切换到文档模式的“标准”时，没有错误。我应该在哪种模式下测试？

如果 IE8 不支持地图功能，有没有办法模拟它？

Answer 1

它不受支持，但MDN提供了一个非常接近规范的 shim：

// Production steps of ECMA-262, Edition 5, 15.4.4.19
// Reference: http://es5.github.com/#x15.4.4.19
if (!Array.prototype.map) {
  Array.prototype.map = function(callback, thisArg) {

    var T, A, k;

    if (this == null) {
      throw new TypeError(" this is null or not defined");
    }

    // 1. Let O be the result of calling ToObject passing the |this| value as the argument.
    var O = Object(this);

    // 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;

    // 4. If IsCallable(callback) is false, throw a TypeError exception.
    // See: http://es5.github.com/#x9.11
    if (typeof callback !== "function") {
      throw new TypeError(callback + " is not a function");
    }

    // 5. If thisArg was supplied, let T be thisArg; else let T be undefined.
    if (thisArg) {
      T = thisArg;
    }

    // 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);

    // 7. Let k be 0
    k = 0;

    // 8. Repeat, while k < len
    while(k < len) {

      var kValue, mappedValue;

      // 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) {

        // i. Let kValue be the result of calling the Get internal method of O with argument Pk.
        kValue = O[ k ];

        // 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);

        // 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;
      }
      // d. Increase k by 1.
      k++;
    }

    // 9. return A
    return A;
  };      
}

Answer 2

使用jQuery.map()：

if (!Array.prototype.map) {   
    Array.prototype.map = function (callback, thisArg) {
        return $.isArray(thisArg) ? $.map(thisArg, callback) : [];
    };
}

Answer 3

IE8 不支持 ES5 数组方法。

您可以使用 jQuery$.map()或下划线_.map()。

---

如果你没有使用这些库中的任何一个，你可以在 MDN 上使用这个 polyfill。

Answer 4

不，它没有实施。但是您可以通过以下方式扩展 Array 原型：

(function(fn){
    if (!fn.map) fn.map=function(f){var r=[];for(var i=0;i<this.length;i++)r.push(f(this[i]));return r}
    if (!fn.filter) fn.filter=function(f){var r=[];for(var i=0;i<this.length;i++)if(f(this[i]))r.push(this[i]);return r}
})(Array.prototype);

Answer 5

请查看ECMAScript 5 兼容性表。IE8 不支持 Array.prototype.map。您可以使用jQuery.map()