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What is an immediately-invoked function in JavaScript?

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Immediately-Invoked Function Expressions (IIFE) are functions that will execute when they are created.

(function(){ 
    console.log("IIFE");
})();
// this will print 'IIFE'

We define a function inside parentheses, and add () to execute that function.


We can also provide a name to the IIFE function.

(function print(){ 
    console.log("IIFE");
})();

The function name is optional for function expression, but it is required for the function declaration.


We can move the () inside the expression parentheses.

(function(){ 
    console.log("IIFE");
})();

// we can also do like
(function(){ 
    console.log("IIFE");
}());

The IIFE must be enclosed inside the parentheses, otherwise, we will get a SyntaxError.

function(){ 
    console.log("IIFE");
}()

To avoid these parentheses, we can add any of these operators (~, +, -, !) before the function keyword.

+function print(){ 
    console.log("IIFE");
}()

-function print(){ 
    console.log("IIFE 1");
}()

When internally adding this operator, JavaScript tries to convert the function to a value, which adds parentheses.


Creating IIFE using arrow function:

(() => {
     console.log("IIFE");
})()

Sending params to IIFE:

((a) => {
     console.log(a); // prints 10
})(10)

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