JavaScript判断数组是否包含指定的元素

JavaScript判断数组是否包含指定的元素，这段代码通过prototype定义了数组方法，这样就可以在任意数组调用contains方法

/**
 * Array.prototype.[method name] allows you to define/overwrite an objects method
 * needle is the item you are searching for
 * this is a special variable that refers to "this" instance of an Array.
 * returns true if needle is in the array, and false otherwise
 */
Array.prototype.contains = function ( needle ) {
   for (i in this) {
       if (this[i] == needle) return true;
   }
   return false;
}

用法

// Now you can do things like:
var x = Array();
if (x.contains('foo')) {
   // do something special
}