Question

var a = function () {
    return 'test';
}();

console.log(a);

Answer in First Case : test

var a = (function () {
    return 'test';
})();

console.log(a);

Answer in Second Case : test

I am using the the first approach to create self-executing functions. However, I have seen the second approach as well. Is there any difference in the two approaches ? The result is obviously the same.

Answer 1

The first syntax is only valid if you assign the result of the function execution to a variable, If you just want to execute the function, this form would be a syntax error:

function(){
   return 'test';
}();

The other form is still valid, though:

(function(){
    return 'test';
 })();

Therefore the second version is more flexible and can be used more consistently.

(The first form is not valid syntax to avoid ambiguities in the Javascript grammar.)