Make the Row TypeScript return type generic

[Ethan-Arrowood]

When using mapValues, you can essentially transform the result of the csv parsing. In order to reflect these changes, one should be able to pass a generic to the neatCsv method that will be used as the resulting data type.

[sindresorhus]

Even better would be to make https://github.com/mafintosh/csv-parser/blob/789e0c13e2cbd705dbdbe263adbdc0493e9b90ec/index.d.ts#L57 generic, so the value defined as return value for the mapValues option, if defined, ends up as the main return value. Can you open an issue/PR on https://github.com/mafintosh/csv-parser about that? I'm happy to merge this in the meantime though.

[Ethan-Arrowood]

Yes happy to do so!

[Ethan-Arrowood]

Even better would be to make https://github.com/mafintosh/csv-parser/blob/789e0c13e2cbd705dbdbe263adbdc0493e9b90ec/index.d.ts#L57 generic, so the value defined as return value for the mapValues option, if defined, ends up as the main return value

What is the goal here? I don't think I'm fully understanding the expected result

/* data.csv
num
1
2
3
4
*/
const csv = require('csv-parser')
const fs = require('fs')

type Row = {
  num: number
}

const results: Row[] = [];

fs.createReadStream('data.csv')
  .pipe(csv<Row>({
    mapValues: ({header, index, value}) => {
      var parsed = parseInt(value)
      return isNaN(parsed) ? -1 : parsed
    }
  }))
  .on('data', (data) => results.push(data)) // is the type of `data` supposed to be `Row`?
  .on('end', () => {
    console.log(results);
    // [
    //   { num: 1 },
    //   { num: 2 },
    //   { num: 3 },
    //   { num: 4 }
    // ]
  });

Because I don't believe that is possible with Node.js types. In this type of code I'd use type casting to indicate what data is, i.e. .on('data', (data) => results.push(data as Row))

[sindresorhus]

My thinking was that mapValues could change the return value of csv(), but I forgot it has to go through a loosely-typed stream in csv-parser, so never mind.