Jquery 实现原理深入学习(3)

1.总体结构 √

2.构建函数 √

3.each功能函数实现 √

4.map功能函数实现 √

5.sizzle初步学习

6.attr功能函数实现

7.toggleClass功能函数实现(好伤)

8.val功能函数实现

9.ajax异步请求以及扩展学习

 Pass each element in the current matched set through a function, producing a new jQuery object containing the return values.
 

// arg is for internal usage only
map: function( elems, callback, arg ) {
	var value,
		i = 0,
		length = elems.length,
		isArray = isArraylike( elems ),
		ret = [];

	// Go through the array, translating each of the items to their new values
	if ( isArray ) { //判断是数组还是对象，数组用for循环，对象用for in遍历其属性.
		for ( ; i 

var arr =[1,2,3];

var arr2 = [4,5];

arr.concat(arr2);//return [1,2,3,4,5]

var deletedIds = [];

var slice = deletedIds.slice;

var concat = deletedIds.concat;

...

var ret = [];
...
ret[ret.length] = value;
...

return ret.concat.apply([],ret);

关键作用的是apply,因为apply的第二个参数把ret的数组分成多个参数传入给concat

作用:把二维数组转化为一维数组

$.map( [0,1,2], function(n){
  return [ n, n + 1 ];
});
//输出：[0, 1, 1, 2, 2, 3]
//如果是return ret的话，输出将会是：[[0,1], [1,2], [2,3]]

   _.map = _.collect = function(obj, iterator, context) {
        // 用于存放返回值的数组
        var results = [];
        if(obj == null)
            return results;
        // 优先调用宿主环境提供的map方法
        if(nativeMap && obj.map === nativeMap)
            return obj.map(iterator, context);
        // 迭代处理集合中的元素
        each(obj, function(value, index, list) {
            // 将每次迭代处理的返回值存储到results数组
            results[results.length] = iterator.call(context, value, index, list);
        });
        // 返回处理结果
        if(obj.length === +obj.length)
        //如果是数组的话，一定要返回相同长度的新数组
            results.length = obj.length;
        return results;
    };

console.log(_.map([1, 2, 3], function(n){ return [ n, n + 1 ]; }));