js怎么实现Array的reduce函数？

Question

js怎么实现Array的reduce函数？

Answer 1

if (!Array.prototype.reduce) {

  Array.prototype.reduce = function(callback /*, initialValue*/) {

    'use strict';

    if (this === null) {

      throw new TypeError('Array.prototype.reduce called on null or undefined');

    }

    if (typeof callback !== 'function') {

      throw new TypeError(callback + ' is not a function');

    }

    var t = Object(this), len = t.length >>> 0, k = 0, value;

    if (arguments.length == 2) {

      value = arguments[1];

    } else {

      while (k < len && !(k in t)) {

        k++; 

      }

      if (k >= len) {

        throw new TypeError('Reduce of empty array with no initial value');

      }

      value = t[k++];

    }

    for (; k < len; k++) {

      if (k in t) {

        value = callback(value, t[k], k, t);

      }

    }

    return value;

  };

}