event-loop.md

#Event Loop Questions To help understand Javascript's Event Loop System. I recommend you to read this book: Secrets of Javascript Ninja https://www.manning.com/books/secrets-of-the-javascript-ninja

###1. setTimeout()

function test() {
    console.log(1);
    setTimeout(function() {
        console.log(2);
    }, 1000);
    setTimeout(function() {
        console.log(3);
    }, 0);
    console.log(4);
}
test();

Answer is: 1, 4, 3, 2. Whatever inside setTimeout will be asigned into the end of event loop. So after 1 was logged, 4 will be the next. Then event loop moves to the 0 and 3.

function test() {
    for (let i = 0; i < 5; i++) {    // we used let in here
        setTimeout(function() {
            console.log(i);
        }, 1000);
    }
}
test();

As we know from chapter closure, a new i was created each loop. Thus the answer is 0, 1, 2, 3, 4. This is exactly what we expect from event loop.

###2. setInterval() What's the difference between the setTimeout and setInternal?

// Taobao Interview Question
// Author: oklai@zhihu
setTimeout(function(){
    /* ... */
    setTimeout(arguments.callee, 10);
}, 10);
setInterval(function(){ 
    /*... */
}, 10);

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###References:

1. 5 More JavaScript Interview Exercises https://www.sitepoint.com/5-javascript-interview-exercises/
2. 有哪些经典的 Web 前端或者 JavaScript 面试笔试题？https://www.zhihu.com/question/19841848