Array indexOf and lastIndexOf method

参见https://developer.mozilla.org/en-US/docs/JavaScript/Reference/global_objects/array/indexof

array.indexOf(searchElement[, fromIndex])

接受一个搜索值（searchElement），将其与数组（array）中的每个元素比较。如果找到该值，返回表示该数组元素的一个索引。如果没有找到，返回-1。

由于IE8不支持indexof，Mozilla针对这一函数的解决方案：

if (!Array.prototype.indexOf) {
    Array.prototype.indexOf = function (searchElement , fromIndex ) {
        "use strict";
        if (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 > 1) {
            n = Number(arguments[1]);
            if (n != n) { // shortcut for verifying if it's NaN
                n = 0;
            } else if (n != 0 && n != Infinity && n != -Infinity) {
                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;
    }
}

var array = [2, 5, 9];
var index = array.indexOf(5); // index is assigned 0
alert(index);
//index = array.indexOf(7); // index is assigned -1

array.lastIndexOf(searchElement[, fromIndex]);

if (!Array.prototype.lastIndexOf)
{
  Array.prototype.lastIndexOf = function(searchElement /*, fromIndex*/)
  {
    "use strict";

    if (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 > 1)
    {
      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);

    for (; k >= 0; k--)
    {
      if (k in t && t[k] === searchElement)
        return k;
    }
    return -1;
  };
}