ES5 Array新方法reduceRight使用实例页面

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代码：

HTML代码：
<p id="result"></p>
JS代码：
var eleResult = document.getElementById("result");
if (!window.console) {
    window.console = {};
}
console.log = function(result) {
    var text = document.createTextNode(result), br = document.createElement("br");
    eleResult.appendChild(text);
    eleResult.appendChild(br);
};

if (typeof Array.prototype.reduceRight != "function") {
  Array.prototype.reduceRight = function (callback, initialValue ) {
    var length = this.length, k = length - 1, previous = initialValue;
    if (typeof initialValue === "undefined") {
        previous = this[length - 1];
        k--;
    }
    if (typeof callback === "function") {
       for (k; k > -1; k-=1) {          
          this.hasOwnProperty(k) && (previous = callback(previous, this[k], k, this));
       }
    }
    return previous;
  };
}

var data = [1, 2, 3, 4];
var specialDiff = data.reduceRight(function (previous, current, index) {
  if (index == 0) {
    return previous + current;
  }
  return previous - current;
});

console.log(specialDiff); // 0

结果：