Why use only a few webpage AJAX to load content?

My Question is: Why don't use more webpages AJAX to load the Webpage content? Because of the fact that you 开发者_开发百科can switch off JS or is there a thought about some security problem ?

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Probably for two reasons:

1. Users with Javascript disabled won't see anything.

2. Pages loaded through AJAX aren't crawl-able by search engines. You want your content to be as accessible as possible so people searching the Web will find your application.

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Because in most cases it doesn't make the site any more comfortable to use (often the effect would be the opposite). "Ajax" shouldn't be used to load entire pages unless you have a very good reason for it.

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One word: SEO. Seach engines execute no javascript -> do not se the content -> do not index the page.