downlevel regexp named capture groups

[jaredh159]

Search Terms

"named capture"
regexp named capture groups

Suggestion

Regexp named capture groups have been added to the ECMA spec. It would be great if typescript could compile these down based on the desired target. Babel already has a plugin to do so:

babel/proposals#35
babel/babel#9345
tc39/ecma262#1027

Use Cases

Writing next-level javascript regular expressions! 😎

And because it's a great feature for readable, maintainable code, and is in the spec.

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

[jaredh159]

Argh, my bad. It looks like you already do this. I had an error I thought was failure to downlevel these named capture groups, but I was wrong. Sorry! 😬

[cascornelissen]

@jaredh159, do you, by any chance, remember what issue caused this for you back then?

I'm working on a project which has es2018 in the compilerOptions.libs array in tsconfig.js and es5 as compilerOptions.target but the compiled files still contain named capture groups.

This is an example of the regex that shows this issue:

/^(?<name>[A-Za-z]+)/

[jaredh159]

@cascornelissen I can't remember, honestly, sorry. I know I was used named capture groups and was getting an error in Safari I think, so I assumed they weren't being transpiled, but I jumped the gun and I had some mostly unrelated other problem that just happened to crop up at the same time that I started using named capture groups, IIRC.