Preventing closure compiler from renaming certain variables

Question

I have a javascript file with a global object that must not be renamed (_gat from the Google Analytics async tracker).

This object must not be renamed by the Google Closure Compiler as Google Analytics looks for a variable with this specific name.

I've looked into the Javascript Doc notations that are mentioned: http://code.google.com/closure/compiler/docs/js-for-compiler.html - However, I cannot find anything regarding the "protection" of a variable.

The problem exists no matter if I use simple or advanced compilation.

How can I ensure that the _gat variable is not renamed?

Solution 1

Using Closure Compiler web app, you can set js_externs. Refer to Advanced Compilation and Externs for more examples.

// ==ClosureCompiler==
// @compilation_level ADVANCED_OPTIMIZATIONS
// @output_file_name default.js
// @js_externs _gat
// ==/ClosureCompiler==

Solution 2

Use the goog.exportSymbol function from base.js. Documentation is here: http://closure-library.googlecode.com/svn/docs/closure_goog_base.js.html

Usage is like

goog.exportSymbol("_gat", _gat)

Solution 3

See http://closuretools.blogspot.com/2011/01/property-by-any-other-name-part-1.html the part about "All Unquoted"

putting certain vars inside ' ' >>> 'bob' prevents them from being renamed by the compiler

Solution 4

If it isn't declared as part of the code you are compiling than an extern declaration is appropriate: http://code.google.com/closure/compiler/docs/api-tutorial3.html#externs

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Comments

[phidah]

Can you elaborate a bit on that please? Where do I find further information?

[Moishe Lettvin]

(Sorry for the terse initial reply, was replying from my phone and my screen-keyboard-fu is weak).

[Noah Sussman]

This is an interesting option. Even when performing ADVANCED_OPTIMIZATIONS, Closure will not rename string references to methods. Eg it will not rename window.foo if referenced like: window['foo']