JavaScript Web Apps and CPU / RAM usage

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http://ubuntuforums.org – There was this Ubuntu App Showdown, and there were applications posted that were made with JavaScript + HTML + CSS, so web apps, which were put into a WebKit window made with Python. In the discussion about the applications I saw some people complaining that the apps can have a pretty big CPU and RAM usage if I remember right(even the small lightweight applications). Is this true and what can be done to possibly prevent or lower those two? (Hardware)