Native String#match declaration incorrect

[milesj]

The declaration here is incorrect:

flow/lib/core.js

Line 250 in 3a65d83

match(regexp: string | RegExp): ?Array<string>;

According to MDN, match returns an array of strings as well as an index and input property.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/match

[alecperkins]

I just ran into this issue. It causes flow to fail at usage of the match_instance.index property:

return `${ source.substring(0, ext_match.index) }.css`;
                                         ^^^^^ property `index`. Property not found in
return `${ source.substring(0, ext_match.index) }.css`;
                               ^^^^^^^^^^^^^^^ Array

[miklass]

Any progress? I've had to do some wacky "any" workarounds and the whole thing felt like a big hack.

[milesj]

@miklass I was actually looking into this this week. However, it seems they don't review PRs often (I have another waiting).

[miklass]

@milesj embrace the hacks :) I've encountered other issues with definitions and behaviors, for example Buffer.isBuffer in node acts like a type check but flow doesn't . Since I'm writing JS code and using the flow comment syntax, it's surprisingly easy to sprinkle lots of "any" cast comments that are blown away in minification step. It's not a great solution, but it allows me to move past the deficiencies in the flow type definitions and focus on real issues in my code

[rstuven]

In the meantime, I suggest you add the following to .flowconfig

[options]
suppress_comment=.*\\$FlowIssue

And then, just before the problematic line, add a comment like this:

const rxa = ''.match(/./);
if (rxa) {
  // $FlowIssue: https://github.com/facebook/flow/issues/2450
  console.log(rxa.index);
}

[milesj]

PR: #3359

[michaelhogg]

Since PR #3359 (9611080) was reverted in commit 3107fb3, I think this issue needs to be reopened.

Also see:

• PR Fixes String#match and RegExp#exec declarations. (#2450) #3007 – Fixes String#match and RegExp#exec declarations
• Duplicate issue regex String .match flow type wrong #3554 – regex String .match flow type wrong

[kesor]

@miklass @milesj I have a hack that does not involve sprinkling any everywhere, just correcting the signature locally using flow-typed/node.js, explained it here - https://stackoverflow.com/questions/48063016/how-to-extend-flow-bin-to-support-new-node-js-methods/48384325

[KevinGrandon]

I believe that this can now be closed due to #6790. @asolove @mrkev Could you help to close this issue?