@ozo/react-rock/public/polyfill-ie8.js

React 移动端开发脚手架，基于CRA3，通用、开箱即用。

// Array.prototype.reduce() in IE8
// Production steps of ECMA-262, Edition 5, 15.4.4.21
// Reference: http://es5.github.io/#x15.4.4.21
// https://tc39.github.io/ecma262/#sec-array.prototype.reduce
if (!Array.prototype.reduce) {
    Object.defineProperty(Array.prototype, 'reduce', {
        value: function(callback /*, initialValue*/) {
            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');
            }

            // 1. Let O be ? ToObject(this value).
            var o = Object(this);

            // 2. Let len be ? ToLength(? Get(O, "length")).
            var len = o.length >>> 0;

            // Steps 3, 4, 5, 6, 7
            var k = 0;
            var value;

            if (arguments.length >= 2) {
                value = arguments[1];
            } else {
                while (k < len && !(k in o)) {
                    k++;
                }

                // 3. If len is 0 and initialValue is not present,
                //    throw a TypeError exception.
                if (k >= len) {
                    throw new TypeError('Reduce of empty array ' + 'with no initial value');
                }
                value = o[k++];
            }

            // 8. Repeat, while k < len
            while (k < len) {
                // a. Let Pk be ! ToString(k).
                // b. Let kPresent be ? HasProperty(O, Pk).
                // c. If kPresent is true, then
                //    i.  Let kValue be ? Get(O, Pk).
                //    ii. Let accumulator be ? Call(
                //          callbackfn, undefined,
                //          « accumulator, kValue, k, O »).
                if (k in o) {
                    value = callback(value, o[k], k, o);
                }

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

            // 9. Return accumulator.
            return value;
        },
    });
}