Usually, people who post this question are trying to use a specific web site, get an error message saying that they should enable JavaScript, and then just post the question. If this is the case here, it would help to know which web site you are talking about. Some web sites may assume that your JavaScript isn't working because of your user agent string, because of a missing JavaScript feature in Internet Explorer Mobile, because it can't open a new window, or for some other reason... there isn't just one single answer to why you might see a message like that.
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