Array对象扩展

虽然现在各大高级浏览器都支持了数组对象的扩展方法，例如some，forEach等，但是为了兼容各低端浏览器，流行框架会添加自己的支持方法，下面列出常用的一些扩展：

	<script>
		Array.prototype.indexOf = function(item, fromIdx){
			var length = this.length;
				fromIdx = fromIdx == null ? 0 : fromIdx < 0 ? Math.max(0, fromIdx + length) : fromIdx;
			for(; fromIdx < length; fromIdx++){
				if(fromIdx in this && this[fromIdx] === item){
					return fromIdx;
				}
			}
			return -1;
		}

		Array.prototype.lastIndexOf = function(item, fromIdx){
			var length = this.length;
				fromIdx = fromIdx == null ? length -1 : fromIdx < 0 ? Math.max(0, fromIdx + length) : fromIdx;
			for(; fromIdx > -1; fromIdx--){
				if(fromIdx in this && this[fromIdx] === item){
					return fromIdx;
				}
			}
			return -1;
		}

		Array.prototype.forEach = function(callback, thisObj){
			thisObj =  thisObj || window;
			for(var i = 0, len = this.length; i < len; i++){
				callback.call(thisObj, this[i], i, this);
			}
		}

		Array.prototype.every = function(callback, thisObj){
			thisObj =  thisObj || window;
			for(var i = 0, len = this.length; i < len; i++){
				if(!callback.call(thisObj, this[i], i, this)){
					return false;
				}				
			}
			return true;
		}

		Array.prototype.some = function(callback, thisObj){
			thisObj = thisObj || window;
			for(var i = 0,len = this.length; i < len; i++){
				if(callback.call(thisObj, this[i], i , this)){
					return true;
				}
			}
			return false;
		}

		Array.prototype.filter = function(callback, thisObj){
			var arr = [];
			thisObj = thisObj || window;
			for(var i = 0,len = this.length; i < len; i++){
				if(callback.call(thisObj, this[i], i , this)){
					arr.push(this[i]);
				}
			}
			return arr;
		}

		Array.prototype.map = function(callback, thisObj){
			thisObj =  thisObj || window;
			for(var i = 0, len = this.length; i < len; i++){
				callback.call(thisObj, this[i], i, this);
			}
		}

		Array.prototype.reduce = function(callback, initVal){
			var i = 0, len = this.length;
			if(!initVal){ //没有初始值则寻找arr里第一个值
				for(;i < len; i++){
					if(i in this){
						initVal = this[i];break;
					}
				}
				if(!initVal){
					throw new Error('no reduce element');
				}
			}
			for(; i < len; i++){
				if(i in this)
					initVal = callback.call(null, initVal, this[i], i, this);
			}
			return initVal;
		}

		Array.prototype.remove = function(obj){//逆序移除 避免splice的时候重置i
			for(var i = this.length - 1; i >= 0; i--){
				if(this[i] === obj){
					this.splice(i, 1);
				}
			}
			return this;
		} 

		Array.prototype.unique = function(){
			for(var i = this.length - 1; i >= 0; i--){
				for(var j = i - 1; j >= 0; j--){
					if(this[i] === this[j]){
						this.splice(j, 1);
						i--;
					}
				}
			}
			return this;
		}

		Array.prototype.unique2 = function(){
			this.sort();
			for(var i = this.length - 1; i > 0; i--){
				if(this[i] === this[i - 1]){
					this.splice(i, 1);
				}
			}
			return this;
		}
	</script>