Why are parenthesis used to wrap a JavaScript function call?

In JavaScript, the functions wrapped with parenthesis are called “Immediately Invoked Function Expressions" or "Self Executing Functions.

The purpose of wrapping is to namespace and control the visibility of member functions. It wraps code inside a function scope and decrease clashing with other libraries. This is what we call Immediately Invoked Function Expression (IIFE) or Self Executing Anonymous Function.

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.