Why in the google analytics tracking code, do they wrap these lines in a closure?
(function() {
var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
})();
Wouldn't it work the same without the parent closure?
It would work the same, but it could easily break other scripts on your page, if you've declared a variable with an identifier used in the Google code.
By wrapping the declaration in a closure, the variables are scoped to the anonymous function and don't leak to the global scope.
For example, consider this example with the new scope:
var ga = "something important for my script"; // Not overwritten in this scope
(function() {
var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
})();
And this example without it:
var ga = "something important for my script"; // Overwritten!
var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
It would work the same as long as there were no global scope variables defined using the same name. Wrapping the code in a closure places it in its own scope so that it is independent from any other code on the page.
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