what is javascript IIFE principle

April 9, 2022

hello i have a one question about IIFE.

I know IIFE’s general method is

(function(){/code/})()

however, recently i found a new method about IIFE

!function(){/code/}() and +function(){/code/}

is also works like IIFE

i think first is ! make value bool, so the code is to true()?

and second + is make value number and that code is trans NaN()?

but two codes(true(),NaN())not working and two new type IIFE works well

i know how that two codes work IIFE please tell me the
procedure

>Solution :

In the cases of !function() {}() and +function() {}() JavaScript will first evaluate the right handside of the given statement/IIFE and then cast the return value of the IIFE to a boolean in case of ! or to type number in case of +.
If the IIFE returns a boolean ! will negate the return value.

Example

console.log(
  !function() {
    return "something";
  }()
); 

/**
!function() {
  return "something";
}()

evaluates to

!"something" and not true() or false()

lastly !"something" is equivalent to false
*/