An Immediately Invoked Function ( known as IIFE and pronounced as IIFY) is a function that runs as soon as it is defined.
Syntax of IIFE :
(function(){
// Do something;
})();
To understand IIFE, we need to understand the two sets of parentheses which are added while creating an IIFE :
First set of parenthesis:
(function (){
//Do something;
})
While executing javascript code, whenever the compiler sees the word “function”, it assumes that we are declaring a function in the code. Therefore, if we do not use the first set of parentheses, the compiler throws an error because it thinks we are declaring a function, and by the syntax of declaring a function, a function should always have a name.
function() {
//Do something;
}
// Compiler gives an error since the syntax of declaring a function is wrong in the code above.
To remove this error, we add the first set of parenthesis that tells the compiler that the function is not a function declaration, instead, it’s a function expression.
Second set of parenthesis:
(function (){
//Do something;
})();
From the definition of an IIFE, we know that our code should run as soon as it is defined. A function runs only when it is invoked. If we do not invoke the function, the function declaration is returned:
(function (){
// Do something;
})
// Returns the function declaration
Therefore to invoke the function, we use the second set of parenthesis. .
