使用IIFE的setTimeout不是异步的吗？

Question

I've found a strange behavior in the following JavaScript code:

 console.log('hi') setTimeout(function(){ console.log('there'); }(), 5000) console.log('I am js'); 

My expected output in the console is:
hi
I am js
there

But it is showing me:
hi
there
I am js

Why is that? If we use an IIFE with setTimeout it does not go through event loop and tasks queue? Could anyone explain the above output? Thanks in advance.

Answer 1

When you define the function, you are executing it in the same step, thus the console log is displayed.

function(){
  console.log('there');
}()

In this case, the argument that setTimeout() receives is the function return value, which is undefined in this case.

I read your code as:

console.log('hi')

var arg = function(){ console.log('there') }(); // arg receives undefined

setTimeout(arg, 5000) // where arg is undefined and not a function

console.log('I am js');

Now, if you had returned another function, it would execute in 5 seconds as expected.

 console.log('hi') var arg = function(){ console.log('there') return function() { console.log('there again') } }(); // arg receives a function setTimeout(arg, 5000) // where arg is a function console.log('I am js');