What is the (function() { } )() construct in JavaScript?

The (function() { } )() construct is an immediately invoked function expression (IIFE). It is a function, which executes on creation.

Syntax

Here’s the syntax −

(function() {
   // code
})();

As you can see above, the following pair of parentheses converts the code inside the parentheses into an expression −

function(){...}

In addition, the next pair, i.e. the second pair of parentheses continues the operation. It calls the function, which resulted from the expression above.