javascript - Why setTimeout(function, 0) is executed after next operation, but not in the moment of calling?

Question

I run this code in JavaScript:

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

But output is:

2
1

Why not vice versa?

Answer 1

The setTimeout() puts all the code in a queue, and then later based on the time, it executes. So you can see the list of procedures to execute as a line of queue. For the above code, you have:

1. setTimeout
2. console.log(2)
3. Callback Functions, if any.
   1. console.log(1)

So, first thing that executes is, initialize the timer. Secondly, the console.log gets executed and you see 2. An interesting thing to note here is, setTimeout waits at least for 4 ms before executing its callback function.