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Put special operators at the beginning of a function

Written byPhuoc Nguyen
23 Feb, 2021
Usually, we can invoke a function by using the form of Immediately Invoked Function Expression (IIFE).
(function (a, b) {
return a + b;
})(4, 2);

// 6
Do you know that we get the same result if we omit the parentheses and put + at the beginning as follow:
+(function (a, b) {
return a + b;
})(4, 2);

// 6
It works because putting `+` at the beginning of function declaration will turn it to an expression, and passing the parameters with `()` at the end will invoke the expression. It is rare to see that code in development, but it is used in the minifications to save the file size. In addition to `+`, you can use other operators such as `-`, `!`, `~` and void in the similar way to invoke a function:
-function() { ... }();
!function() { ... }();
~function() { ... }();
void function() { ... }();
Note that the return value could be different from the original function, for example:
!(function () {
return false;
})(); // true

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Phước Nguyễn