Fix errors array concatenation

[mdnfiras]

When no error is present, combinedErrors will be equal to [ [ ] , [ ] , ..... , [ ] ] (array of empty arrays), and therefore the check for errors with combinedErrors.length > 0 will always be true (combinedErrors.length = number of inside arrays) and will trigger the denial of the request.

This PR will fix how error strings are concatenated so that combinedErrors will be equal to [ ] when no error is present, and ["error 1", "error 2", .... , "error n"] when errors are present.

the issue is described more here #9

[baracoder]

Changing [].concat.apply(errors) to [].concat.apply([], errors) should be enough

[mdnfiras]

npm run compile produces errors with const combinedErrors: string[] = [].concat.apply([], errors)

running in the node:10 container:

> @jspolicy/jspolicy-typescript-starter@0.0.1 compile /work
> tsc && npm run bundle

src/util/helpers.ts:2:58 - error TS2345: Argument of type 'string[][]' is not assignable to parameter of type 'ConcatArray<never>[]'.
  Type 'string[]' is not assignable to type 'ConcatArray<never>'.
    The types returned by 'slice(...)' are incompatible between these types.
      Type 'string[]' is not assignable to type 'never[]'.
        Type 'string' is not assignable to type 'never'.

2     const combinedErrors: string[] = [].concat.apply([], errors)
                                                           ~~~~~~


Found 1 error.

npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! @jspolicy/jspolicy-typescript-starter@0.0.1 compile: `tsc && npm run bundle`
npm ERR! Exit status 2
npm ERR! 
npm ERR! Failed at the @jspolicy/jspolicy-typescript-starter@0.0.1 compile script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /root/.npm/_logs/2022-03-22T15_57_55_787Z-debug.log

[mdnfiras]

@baracoder however, const combinedErrors: string[] = Array<string>().concat.apply([], errors) also worked, should I write this instead?

EDIT: force pushed to implement const combinedErrors: string[] = Array<string>().concat.apply([], errors) instead

[baracoder]

Sorry, I should have tested it in the actual code instead of Chrome's console 😅
Found an alternative though: errors.flat(), see MDN

[mdnfiras]

@baracoder yup, a newer PR also solves this same issue using errors.flat()
#28

[semmet95]

I ran into the same issue. I know nothing about TypeScript so took me half a day to realize I wasn't the one messing things up. I initialized combinedErrors as following and that worked out for me:

const combinedErrors: string[] = errors.reduce((accumulator, value) => accumulator.concat(value), []);

I hope they merge this PR soon.

[merusso]

#28 also fixes this, by using errors.flat()