feat: add helper for matching function strings

[ojeytonwilliams]

Checklist:

• I have read freeCodeCamp's contribution guidelines.
• My pull request has a descriptive title (not a vague title like Update index.md)

TODO

• Docs
• Return RegExp instead of string (it's trivial to combine them with other regexes)
• Test against fcc curriculum

The docs should explain this pretty well, but the gist is: this function provides a regex to match function expressions/declarations and arrow functions.

[naomi-lgbt]

Can we add an option to not look for the closing bracket?

That is, I would want to be able to test:

const naomi = (love) => {
  return love ** 2
}

With something like

const regex = new RexExp(`${__helpers.functionRegex("naomi", ["love"], {closed: false})}\s*return\s*love\s*\*\*\s*2)`);
assert.match(code, regex);

[ojeytonwilliams]

Sure! Just to check, do you want something that matches everything up to and including the opening bracket (if there is one)?

e.g.

let codeOne = `const naomi = (love) => {
  return love ** 2
}`
let codeTwo = `function naomi(love) {
  return love ** 3
}`
let trickyArrowCode = `const naomi = love => love**2`

let startRE = functionRegex("naomi", ["love"], { closed: false });

startRE.test(codeOne); // true
startRE.test(codeTwo): // true

let fullRE = new RegExp(startRE.source + /\s*return\s*love\s*\*\*\s*2}/.source)

fullRE.test(codeOne); // true
fullRE.test(codeTwo); // false

let weirdRE = new RegExp(startRE.source + /\s*return\s*love/.source)

weirdRE.test(codeOne); // true
weirdRE.test(codeTwo); // true

let arrowRE = new RegExp(startRE.source + /\s*love\*\*2/.source)
arrowRE.test(trickyArrowCode); // true

[ojeytonwilliams]

@naomi-lgbt I'm revisiting this, are those specs more or less what you wanted?

[naomi-lgbt]

Yes that looks great! Thanks!

[ojeytonwilliams]

Hey @naomi-lgbt I think it's worked as intended now. There's still the ugly case where it captures too much (described in the docs), but I can't think of a way around that just using regexes. At least not in the time I allocated myself for this!

It should work well enough for our uses and tide us over until we can incorporate the ast-based tooling Shaun created.

[naomi-lgbt]

This should be fine as is