ECMAScript5 新特性(四)

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if (!Array.prototype.indexOf) { Array.prototype.indexOf = function(searchElement /*, fromIndex */) { "use strict"; if (this === void 0 || this === null) throw new TypeError(); var t = Object(this); var len = t.length >>> 0; if (len === 0) return -1; var n = 0; if (arguments.length > 0) { n = Number(arguments[1]); if (n !== n) n = 0; else if (n !== 0 && n !== (1 / 0) && n !== -(1 / 0)) n = (n > 0 || -1) * Math.floor(Math.abs(n)); } if (n >= len) return -1; var k = n >= 0 ? n : Math.max(len - Math.abs(n), 0); for (; k < len; k++) { if (k in t && t[k] === searchElement) return k; } return -1; };}Function 17: Array.prototype.lastIndexOf用法和16相似，取得最后一次出现参数的index如果浏览器没有实现此方法，你可以通过这种方式实现if (!Array.prototype.lastIndexOf) { Array.prototype.lastIndexOf = function(searchElement /*, fromIndex*/) { "use strict"; if (this === void 0 || this === null) throw new TypeError(); var t = Object(this); var len = t.length >>> 0; if (len === 0) return -1; var n = len; if (arguments.length > 0) { n = Number(arguments[1]); if (n !== n) n = 0; else if (n !== 0 && n !== (1 / 0) && n !== -(1 / 0)) n = (n > 0 || -1) * Math.floor(Math.abs(n)); } var k = n >= 0 ? Math.min(n, len - 1) : len - Math.abs(n); while (k >= 0) { if (k in t && t[k] === searchElement) return k; } return -1; };}

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function isBigEnough(element, index, array) {return (element >= 10);}var passed = [12, 5, 8, 130, 44].every(isBigEnough);// passed is falsepassed = [12, 54, 18, 130, 44].every(isBigEnough);// passed is true

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?当浏览器没有实现此方法时，可以用以下方式代替

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if (!Array.prototype.every) {  Array.prototype.every = function(fun /*, thisp */) {    "use strict";    if (this === void 0 || this === null)            throw new TypeError();    var t = Object(this);    var len = t.length >>> 0;    if (typeof fun !== "function")             throw new TypeError();    var thisp = arguments[1];    for (var i = 0; i < len; i++) {              if (i in t && !fun.call(thisp, t[i], i, t))                return false;    }    return true;  };}

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function isBigEnough(element, index, array) { return (element >= 10);}var passed = [2, 5, 8, 1, 4].some(isBigEnough);// passed is falsepassed = [12, 5, 8, 1, 4].some(isBigEnough);// passed is true

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当浏览器不支持的时候，你可以用以下代码代替

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if (!Array.prototype.some) {  Array.prototype.some = function(fun /*, thisp */) {    "use strict";    if (this === void 0 || this === null)              throw new TypeError();    var t = Object(this);    var len = t.length >>> 0;    if (typeof fun !== "function")              throw new TypeError();    var thisp = arguments[1];    for (var i = 0; i < len; i++) {      if (i in t && fun.call(thisp, t[i], i, t))        return true;    }    return false;  };}

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function printElt(element, index, array) { print("[" + index + "] is " + element); // assumes print is already defined}[2, 5, 9].forEach(printElt);// Prints:// [0] is 2// [1] is 5// [2] is 9

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?当浏览器没有实现的时候，你可以通过如下方法代替

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if (!Array.prototype.forEach) {  Array.prototype.forEach = function(fun /*, thisp */) {    "use strict";    if (this === void 0 || this === null)              throw new TypeError();    var t = Object(this);    var len = t.length >>> 0;    if (typeof fun !== "function")              throw new TypeError();    var thisp = arguments[1];    for (var i = 0; i < len; i++) {      if (i in t)        fun.call(thisp, t[i], i, t);    }  };}

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function makePseudoPlural(single) { return single.replace(/o/g, "e");}var singles = ["foot", "goose", "moose"];var plurals = singles.map(makePseudoPlural);// plurals is ["feet", "geese", "meese"]// singles is unchanged?

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Sample2

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var numbers = [1, 4, 9];var roots = numbers.map(Math.sqrt);// roots is now [1, 2, 3]// numbers is still [1, 4, 9]

如果浏览器没有实现，则可以用如下方法代替

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if (!Array.prototype.map) {  Array.prototype.map = function(fun /*, thisp */) {    "use strict";    if (this === void 0 || this === null)            throw new TypeError();    var t = Object(this);    var len = t.length >>> 0;    if (typeof fun !== "function")            throw new TypeError();    var res = new Array(len);    var thisp = arguments[1]; for (var i = 0; i < len; i++) {             if (i in t)                     res[i] = fun.call(thisp, t[i], i, t);    }    return res;};

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function isBigEnough(element, index, array) {return (element >= 10);}// 12, 130, 44var filtered = [12, 5, 8, 130, 44].filter(isBigEnough);

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?如果浏览器没有实现，则可以用如下方式代替:

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if (!Array.prototype.filter) {Array.prototype.filter = function(fun /*, thisp */) {"use strict";    if (this === void 0 || this === null)              throw new TypeError();    var t = Object(this);    var len = t.length >>> 0;    if (typeof fun !== "function")              throw new TypeError();    var res = [];    var thisp = arguments[1];    for (var i = 0; i < len; i++) {              if (i in t) {        var val = t[i]; // in case fun mutates this        if (fun.call(thisp, val, i, t))          res.push(val);    }}return res;};}

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var total = [0, 1, 2, 3].reduce(function(a, b){ return a + b; });// total == 6var flattened = [[0, 1], [2, 3], [4, 5]].reduce(function(a, b) {return a.concat(b);});// flattened is [0, 1, 2, 3, 4, 5]?

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如果浏览器没有实现，则可用以下代码代替

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if (!Array.prototype.reduce) {  Array.prototype.reduce = function(fun /*, initialValue */) {    "use strict";    if (this === void 0 || this === null)             throw new TypeError();    var t = Object(this);    var len = t.length >>> 0;    if (typeof fun !== "function")             throw new TypeError();    // no value to return if no initial value and an empty array    if (len == 0 && arguments.length == 1)             throw new TypeError();    var k = 0;    var accumulator;    if (arguments.length >= 2) {             accumulator = arguments[1];    } else {             do {        if (k in t) {          accumulator = t[k++];          break;        }        // if array contains no values, no initial value to return                if (++k >= len)          throw new TypeError();              } while (true);    }    while (k < len) {              if (k in t)        accumulator = fun.call(undefined, accumulator, t[k], k, t);              k++;    }    return accumulator;};}

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var total = [0, 1, 2, 3].reduceRight(function(a, b) { return a + b; });//total == 6var flattened = [[0, 1], [2, 3], [4, 5]].reduceRight(function(a, b) { return a.concat(b);}, []);// flattened is [4, 5, 2, 3, 0, 1]?如果浏览器没有实现，则可以用如下代码代替

if (!Array.prototype.reduceRight) {  Array.prototype.reduceRight = function(callbackfn /*, initialValue */) {    "use strict";    if (this === void 0 || this === null)              throw new TypeError();    var t = Object(this);    var len = t.length >>> 0;    if (typeof callbackfn !== "function")              throw new TypeError();    // no value to return if no initial value, empty array    if (len === 0 && arguments.length === 1)              throw new TypeError();    var k = len - 1;    var accumulator;    if (arguments.length >= 2) {              accumulator = arguments[1];    } else {              do {                if (k in this) {          accumulator = this[k--];          break;        }        // if array contains no values, no initial value to return                if (--k < 0)                  throw new TypeError();               } while (true);    }    while (k >= 0) {                if (k in t)        accumulator = callbackfn.call(undefined, accumulator, t[k], k, t);                k--;    }return accumulator;  };}

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1 楼 panxi620 2011-05-11 虽然是教学，但是能否下次贴字上来大些，很伤眼睛