Interesting javascript hack, you should know

1. Javascript Closures

A closure is an inner function that accesses to the outer function’s variables.
It has three scopes (access variables)

• Own scope (variables defined between its curly brackets)
• Outer function’s variables
• Global variables

Note: will amaze with the output of this code, because most of the developer think its output is 0.

Example :

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

Output:

3  

Tried in console

2. Async Javascript -setTimeout function within closure

Example :

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

Output:

 1
 3
 undefined
 2

These are some tricky javascript concept asked in google and amazon interview's

Amazon web developer interview question https://www.reddit.com/r/javascript/comments/7535tm/amazon_web_developer_loop_timeout_interview/