Javascript: !function (x) {}

Question

What does "!" mean here, in front of "function"?

var a = 5
!function (x) {
a = x;
}(7);

Answer 1

Use cases:
- Code Golfing.
- JS minifiers.
It's used for the sole purpose of reducing the number of characters by 1.

Otherwise the classics (function())() or (function()()) are preferred because of better readability.

Answer 2

In this snippet, the unary operator(!) is replacing the parens that normally surrounds the function to create an Immediately-invoked Function Expression (IIFE). You may see other unary operators (+, ~, -, void) used in the same.

JavaScript Immediately-invoked Function Expressions (IIFE)
https://flaviocopes.com/javascript-iife/

JavaScript Unary Operators: Simple and Useful
https://scotch.io/tutorials/javascript-unary-operators-simple-and-useful

https://code.sololearn.com/cIsuovG1mCyh/#node

Answer 3

https://stackoverflow.com/questions/9267289/what-does-function-in-javascript-mean

Similar like calling anonymous function but I didn't checked that we could use ! instead of ( until now!!

(function(){
})()

Answer 4

It makes no sense until you assign the function call expression to something ...

b = !function(x){ ... }(7);

Somehow the function was executed, *perhaps* because JS sees that the function's return value was needed as operand for logical NOT operator.

But Idk what value was returned as I see nothing was being returned. Log test in console said that !<function-call-expression> evaluates to `true` BTW ...