Does named closures pollute the global/window object?

Question

Does named closures pollute the global/window object?

According to this node style guide, giving closures a name is a good practice:

Right

req.on('end', function onEnd() {
  console.log('winning');
});

Wrong

req.on('end', function() {
  console.log('losing');
});

However, I'm used to thinking of the

function someName() { someStatements(); }

...syntax as something that creates a global variable, someName or window.someName for that function. Is this really a good practice, or is that a very bad style guide?

javascript
node.js
coding-style
v8

Answer 1

Although you will not have this problem with node:

named function expressions are bugged in Internet Explorer, and will pollute the window object, as explained here: http://kangax.github.com/nfe/ under "JScript bugs"

The (not so) funny thing is that they are created even within conditional blocks that are never executed, as in this example:

var f = function g() {
  return 1;
};
if (false) {
  f = function g(){
    return 2;
  };
}
g(); // 2

This has created a problem on a production site I worked with, where jQuery suddenly was replaced with something else ( https://dev.plone.org/ticket/12583 )

Answer 2

In node.js, what you describe does not pollute the global context.

Given:

function someName() { someStatements(); }

global.someName will be defined. The following however:

setTimeout(function someName() { someStatements(); }, 500);

Will not set global.someName.

It seems to be just a matter of aesthetics. I tested this with node.js v0.8.4, but the same behaviour should be present in most modern browsers.

Answer 3

You can't access anonymous function using name (if function has name). It would be accessible within function body. So it would not pollute the window object.

req.on('end', function onEnd() { 
  console.log(onEnd); //function body
}); 
console.log(onEnd); //ReferenceError: onEnd is not defined

Answer 4

The name of named closure is only accessible inside of this closure so it should never pollute global namespace. Normally you would use the named closure to create a recursive closure.