Awkward way of executing JavaScript code

Question

In the Google tutorial for implementing Google+ sign-in in Flask application, I discovered that the developer often uses an awkward way of executing JavaScript code:

Instead of doing

var a = foo(bar);

I see this:

var a = (function() {
  return foo(bar);
})();

What is the reason to do it the weird way?

There's no reason to use that syntax there, and it doesn't appear on the page you link to. Could you link to the actual example so we can see the context? — Quentin, Feb 03 '14 at 13:09
Oh, ok, so it's just not to leave garbage of once needed but now obsolete variables behind. — Passiday, Feb 03 '14 at 13:13
@Quentin the actual code in the tutorial is very large and thus too specific to be included in the question. — Passiday, Feb 03 '14 at 13:15

score 52 · Accepted Answer · edited Oct 10 '22 at 06:29

This is a poor example. Consider the following:

var a = (function() {
  var ret = {};
  ret.test = "123";

  function imPrivate() { /* ... */ }
  ret.public = function() {
    imPrivate();
  }
  return ret;
})();

console.log(a)

a will contain the varible test and the function public, however you can not access imPrivate. This is the common way to handle public vs private variables;

See Why is this function wrapped in parentheses, followed by parentheses? for more info.

score 10 · Answer 2 · edited Dec 12 '17 at 08:19

10

var a = (function() {
  return foo(bar);
})();

In this case this is really unnecessary, but this is not wrong and it will not throw an error.

But IIF some times uses like module pattern:

var a = (function() {
  /* some other code in own scope */
  return foo(bar);
})();

In this case IIF is just a module which exports something outside.

edited Dec 12 '17 at 08:19

Or A.

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answered Feb 03 '14 at 13:08

Alex

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score 2 · Answer 3 · answered Feb 03 '14 at 13:13

2

The closure function is used to encapsulate some of the attributes / methods in the function. Much like the private / public principle from other languages.

You can find more on this topic here under Module Pattern

answered Feb 03 '14 at 13:13

Anonymoose

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Awkward way of executing JavaScript code

3 Answers3