how does google crawler read javascript?thanks..

I don't think Google or any other crawler has the ability to understand Javascript, as they are not like users when they visit a site, they are grabbing content, not performing actions, events, etc that triggers Javascript.

Since you're asking this, I guess it's because you'd like to use Javascript and still have pages crawled. This is where you must think about your javascript design. Allways provide a fall back. An example would be like this:

<a href="thispage.php" onclick="goto('thispage.php');return false;">This Page</a>

For those with javascript enabled, the onclick will take over the action for that link, which means if I were using AJAX I could automatically grab the content and write the page without it reloading the whole page again, making it feel quicker for that user. If javascript however isn't enabled, then the href attribute will take over and send them to the page, with page reload but they still have access to the same content. This is the link google would crawl and all other people with javascript turned off, as long as you provide a fallback means your site will still be accessible.

One thing that people also say is that doing this breaks the ability for a person to bookmark the page, well it does but it's not too much of an effort to provide a script so they can easily bookmark the site, so that is really a small complaint that can easily be fixed and other complaints, possibly have alternative solutions too.

Cheers,

MC

I am not sure. But i think all crawler just skip <script> tag. But google crawler tries to read SWFs to find links!!

I think that google crawler read javascript by using script tags.

All search engine indexers can read the code between <script> </script> tags, but they cannot execute the script commands.