Is it possible to load one particular file from localhost?

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http://stackoverflow.com – In my application statics files are loading from proxy server I want to load one JS file from my localhost so that I can edit and test it with my production app. For example:- www.staticserver.com/39349/file.js localhost/xyz/file.js can I do it in /etc/hosts file or any browser plug-in ? (HowTos)