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：
1 if (!Array.prototype.indexOf) { 2 Array.prototype.indexOf = function (searchElement , fromIndex ) { 3 "use strict"; 4 if (this == null) { 5 throw new TypeError(); 6 } 7 var t = Object(this); 8 var len = t.length >>> 0; 9 if (len === 0) { 10 return -1; 11 } 12 var n = 0; 13 if (arguments.length > 1) { 14 n = Number(arguments[1]); 15 if (n != n) { // shortcut for verifying if it's NaN 16 n = 0; 17 } else if (n != 0 && n != Infinity && n != -Infinity) { 18 n = (n > 0 || -1) * Math.floor(Math.abs(n)); 19 } 20 } 21 if (n >= len) { 22 return -1; 23 } 24 var k = n >= 0 ? n : Math.max(len - Math.abs(n), 0); 25 for (; k < len; k++) { 26 if (k in t && t[k] === searchElement) { 27 return k; 28 } 29 } 30 return -1; 31 } 32 } 33 34 var array = [2, 5, 9]; 35 var index = array.indexOf(5); // index is assigned 0 36 alert(index); 37 //index = array.indexOf(7); // index is assigned -1
array.lastIndexOf(searchElement[, fromIndex]);
1 if (!Array.prototype.lastIndexOf) 2 { 3 Array.prototype.lastIndexOf = function(searchElement /*, fromIndex*/) 4 { 5 "use strict"; 6 7 if (this == null) 8 throw new TypeError(); 9 10 var t = Object(this); 11 var len = t.length >>> 0; 12 if (len === 0) 13 return -1; 14 15 var n = len; 16 if (arguments.length > 1) 17 { 18 n = Number(arguments[1]); 19 if (n != n) 20 n = 0; 21 else if (n != 0 && n != (1 / 0) && n != -(1 / 0)) 22 n = (n > 0 || -1) * Math.floor(Math.abs(n)); 23 } 24 25 var k = n >= 0 26 ? Math.min(n, len - 1) 27 : len - Math.abs(n); 28 29 for (; k >= 0; k--) 30 { 31 if (k in t && t[k] === searchElement) 32 return k; 33 } 34 return -1; 35 }; 36 }
