Regex selection in another selection

Question

so I have a string like this:

var a = " 'asdf'+'asdf'+'we' + 1";

I am able to select the three quotes with:

'([^']*)'

How do I select the start of the single quote(') in the string using regex? And also a separate regex to select the end of the single quote(')? Is this possible with regex? I will replace the start of the quote with <<.

Final string will look like

 " <<asdf'+<<asdf'+<<we' + 1"

Answer 1

When you need to replace some part of a pattern only, use capturing group round the part you need to keep, and just match (and consume) those parts you need to remove.

var a = " 'asdf'+'asdf'+'we' + 1";
console.log(
    a.replace(/'([^']*')/g, '<<$1')
);
// And, to replace both ' in one go (notice the ) shift to the left):
console.log(
    a.replace(/'([^']*)'/g, '<<$1>>')
);

Here,

• ' - matches and consumes '
• ([^']*') - matches and captures into Group 1 zero or more chars other than ' (with [^']*) and then a '. The $1 in the replacement pattern is a placeholder for the contents stored in Group 1 after a valid match is found.
• ([^']*) - only captures any 0+ chars other than ' into Group 1 so, the final ' is matched and consumed, and will be missing in the $1 placeholder content.

Also, see the regex demo 1 and regex demo 2.