The ! symbol shows that it is an immediately-invoked function expression.
The exclamation mark won’t invoke the function alone; you can put () at the end −
!function foo() {}()() has higher precedence than ! and instantly calls the function.
You can also mention it like the following −
(function(){})();The ! allows the expression to return true. This is because by default all immediately-invoked function expression return undefined, so, we’re left with ! undefined, which is true.