Lookahead in JavaScript regex

问题

Using JavaScript, I am trying to replace an attribute inside an html tag, and have come up with this regex:

/<\s*tag[^>]*(attr)=['"]{1,1}([^'"\s]*)['"]{1,1}/ig;

This works. However, I want to be able to specify to look for the same type of quotation mark enclosing the attribute value. So, for example, I want to specify if this is the form <tag attr='data'>, to look in the SECOND quotation mark for the single one, not the double one. The inverse case, <tag attr="data"> would be similar; match the SECOND mark with double quotes, not single ones. This is to help me protect the function call against strangely formed HTML.

So, how can I achieve this?

Thanks!

回答1:

Try this:

/<tag[^>]*attr=(['"])(?:(?!\1)\S)*\1/ig;

Explanation:

<tag     # Match <tag (\s* is not needed since whitespace is illegal here)
[^>]*    # Match any non-> characters
attr=    # Match "attr="
(['"])   # Match a quote, remember which kind; {1,1} can be dropped (it's a no-op)
(?:      # Try to match
 (?!\1)  #  (unless it's the corresponding closing quote)
 \S      #  any non-whitespace character
)*       # any number of times
\1       # Match the corresponding closing quote

回答2:

Try this:

/<\s*tag[^>]*(attr)=(['"]{1,1})([^'"\s]*)\2{1,1}/ig;

来源：https://stackoverflow.com/questions/12466262/lookahead-in-javascript-regex