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Asked: 2026-06-05T08:20:59+00:00

Before you quickly post with RTFM or with a bunch of links I have

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Before you quickly post with “RTFM” or with a bunch of links I have visited, I am fully aware of the documented reserved variable names not to use.

The best lists I could find are here:

http://es5.github.com/x7.html#x7.6.1.1
and
http://www.javascripter.net/faq/reserved.htm

What I am asking for are the variable names that are invalid on 1 or 2 browsers only.

For example I can define print but this will cause an error as print is already defined on the global scope window. Why isn’t this documented as a reserve keyword?

Is there a big list of variable names to avoid?

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  1. Editorial Team

    If you want a big list of browser-defined variables to extend the official list of reserved keywords, type the following into your console on an empty page (about:blank):

    >>> Object.getOwnPropertyNames(window)
>>> Object.getOwnPropertyNames(Object.getPrototypeOf(window)) // sometimes not Object

    which will yield an Array of strings you definitely should not use. It includes "print", too.

    Yet it will be browser-dependent, because some do not implement all the cool HTML5-drafted stuff that uses the Window interface; e.g. you won’t find "Worker" in IE9, "openDatabase" in FF and so on. Also, it might not list legacy properties like "onload", altough you will be able to to get a property descriptor for it (and "onload" in window === true).

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