数组的slice方法和类数组

https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/slice

slice 方法可以用来将一个类数组（Array-like）对象/集合转换成一个数组。你只需将该方法绑定到这个对象上。下述代码中 list 函数中的 arguments 就是一个类数组对象。

function list() {  return Array.prototype.slice.call(arguments);}var list1 = list(1, 2, 3); // [1, 2, 3]

/*** Shim for "fixing" IE's lack of support (IE < 9) for applying slice* on host objects like NamedNodeMap, NodeList, and HTMLCollection* (technically, since host objects have been implementation-dependent,* at least before ES6, IE hasn't needed to work this way).* Also works on strings, fixes IE < 9 to allow an explicit undefined* for the 2nd argument (as in Firefox), and prevents errors when* called on other DOM objects.*/(function () {    'use strict';    var _slice = Array.prototype.slice;    try {        // Can't be used with DOM elements in IE < 9        _slice.call(document.documentElement);    } catch (e) { // Fails in IE < 9        // This will work for genuine arrays, array-like objects,        // NamedNodeMap (attributes, entities, notations),        // NodeList (e.g., getElementsByTagName), HTMLCollection (e.g., childNodes),        // and will not fail on other DOM objects (as do DOM elements in IE < 9)        Array.prototype.slice = function (begin, end) {            // IE < 9 gets unhappy with an undefined end argument            end = (typeof end !== 'undefined') ? end : this.length;            // For native Array objects, we use the native slice function            if (Object.prototype.toString.call(this) === '[object Array]'){                return _slice.call(this, begin, end);            }                       // For array like object we handle it ourselves.            var i, cloned = [],                size, len = this.length;                       // Handle negative value for "begin"            var start = begin || 0;            start = (start >= 0) ? start: len + start;                       // Handle negative value for "end"            var upTo = (end) ? end : len;            if (end < 0) {                upTo = len + end;            }                       // Actual expected size of the slice            size = upTo - start;                       if (size > 0) {                cloned = new Array(size);                if (this.charAt) {                    for (i = 0; i < size; i++) {                        cloned[i] = this.charAt(start + i);                    }                } else {                    for (i = 0; i < size; i++) {                        cloned[i] = this[start + i];                    }                }            }                       return cloned;        };    }}());

网上的习题：

var slice = Array.prototype.slice; alert(slice.call({0: 'foo', length: 'bar'})[0]); // 当length值不能转化为有效的数字时，返回一个空数组alert(slice.call(NaN).length); //0 alert(slice.call({0: 'foo', length: '100'})[0]); // 返回一个长度为100的数组，第一个元素是‘foo’

var obj = {"2" : "a","3" : "b",    "length" : 2,    "push" : Array.prototype.push}   obj.push('c');obj.push('d');console.log(obj);//Object {2: "c", 3: "d", length: 4, push: function}

解释：

Array.prototype.push = function(target){this[this.length] = target;this.length++; }

类数组：属性必须是数字索引，且必须有length属性。