JS return function

Question

function firstLoad() {
	var _list=[];
	return function(id) {
		if(_list.indexOf(id)>=0){
			return false;
		}else {
			_list.push(id);
			console.log(_list);
		}
	}
}
var first=firstLoad();
first(10);
first(10);
first(11);

在这个地方为啥要return function？为啥去掉return之后会报错？

Answer 1

因为 var first=firstLoad();   就是得到firstLoad 这个方法的返回值，然后赋给 first ;   也就是这个first就是 方法firstLoad 的返回值，如果你不加return ，方法默认传回的就是undefined; 你后面的这三行就是执行一个方法 first(10);first(10);first(11); 没有返回 frist就是undefined,它不是一个方法，就不能执行，就报错了。

Answer 2

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