How do you exclude specific groups from $N when using RegExp?

I managed to create a regex that works, but I believe there may be a better use-case:

element = '<div style="color:red">123</div>';
element.replace(/(<div.*>)(\d+)(<\/div>)/g, '$1<b>$2</b>$3');
// expecting output: <div style="color:red"><b>123</b></div>

After doing some research, I discovered that (?: ... ) in regex means to ignore group matches, like this:

element.replace(/(?:<div.*>)(\d+)(?:<\/div>)/g, '<b>$1</b>');
// returns <b>123</b>

However, I still want my expected result from the 1st example.

Is there a way to exclude them? Can we simply write

replace(/.../, '<b>$1</b>')
?

This is just a simple case to understand how to exclude groups in regex. And yes, I'm aware that we can't parse HTML with regex :)

Answer №1

Are you looking to achieve the same outcome using only the replacement <strong>$1</strong>?

If that's the case, simply use

replace(/\d+/, '<strong>$&</strong>')
.

In order to ensure that the number is surrounded by div tags, you would need to implement lookarounds and the \K feature as shown below. However, it's worth noting that JS does not support lookbehind or \K, so a capturing group must be used instead.

<div[^>]*>\K\d+(?=</div>)

Answer №2

There is no issue with using the replacement value of '$1<b>$2</b>$3'. You just need to adjust your regex pattern like this:

el = '<div style="color:red">123</div>';
el.replace(/(<div[^>]*>)(\d+)(<\/div>)/g, '$1<b>$2</b>$3');

By changing how it matches the first div tag, you ensure that it captures the minimum possible content before the closing > of the tag instead of the maximum.

Your current regex might not give you the desired result with this input string:

el = '<div style="color:red">123</div><div style="color:red">456</div>';

The downside of using something like:

el.replace(/\d+/, '<b>$&</b>')

is that it doesn't handle cases like this properly:

el = '<div style="margin-left: 10px">123</div>'

This is because it picks up numbers within the div tags instead of outside them.

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