JavaScript闭包和for循环

Question

I was wondering why the result of the following code is 0 and not 3.

var fn = function(){
    for (i = 0; i < 3; i++){
        return function(){
            console.log(i);
        };
    }
}();

fn();

Answer 1

Because your return statement forces the loop to terminate and the function to stop executing.

You can learn more about return statements here - https://en.wikipedia.org/wiki/Return_statement

Answer 2

You're returning a closure that's calling console.log . When you're doing this return statement you're stopping fn() from proceeding, it returns the first thing that needs returning and halts execution. Remove the return statement (and closure) if you want to console.log.

var fn = function(){
    for (i = 0; i < 3; i++){
        console.log(i);
    }
}();

fn();

Also See: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Statements/return