This uses JavaScript to switch between CSS files for the different sizes. The advantage is that the CSS files can be kept very seperate. The disadvatage is that because the CSS files are totally seperate, there will be more files to update when changes need to be made. An idea is to put the styles that are common in a single CSS file and then put only the responsive parts in the switching CSS files. That does leave the question, why are you using this instead of media queuries in CSS? Is it a browser support requirement?
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