Improve JS Regex to exclude lines that contain a certain string

Question

I have a JS regex to replace sections of a string that include img tags inside p tags. I'm picking up ones I don't want.

Sample of what I want to find and replace (the src and class are not always in the same order and imageData is not always the same base64 "numbers", so I can't just match on the whole string):

<p><img class="classIWantToMatch" src="data:image/gif;base64,dataForImage"></p>
<p><img src="data:image/gif;base64,imageData" class="classIWantToMatch" ></p>

Sample that is also getting found and replaced (but I don't want to):

<p><img src="/myFiles/my.PNG" alt=""></p>

Regex:

/(<p><img).*?(class="classIWantToMatch").*?(<\/p>)/g

I'm trying to figure out lookahead and lookbehind, but I can't seem to make it do what I want.

Besides ye olde basic googling, I tried here:

A Regex that search for lines that contains a string, and not contains another string

Using Regex to find string that contains one string and excludes a second string?

and several other ones as well. I think I just don't understand lookahead/behind.

Answer 1

This RegEx might help you to only get your desired target or design an expression to do so:

(<p><img.+class=\")(classIWantToMatch)(\".+<\/p>) 

• You can only bound your desired target in second capturing group.
• With a simple left boundary as (<p><img.+class=\") and right boundary as (\".+<\/p>) you might be able to do so. However, you might consider making these boundaries more restrictive just to be safe. For instance, .+ can be much limited to a list of chars.