Parametrized classes

type OutputFormat = 'csv' | 'ndjson'
abstract class Output<Format extends OutputFormat> {
  format: Format
  constructor(format: string) {
    this.format = format
  }
  abstract encode(data: any[]): string
}
class CSV extends Output<'csv'> {
  constructor() {
    super('csv')
  }
  encode(data: any[]) {
    return data.map((row) => row.join(',')).join('\n')
  }
}
class NDJSON extends Output<'ndjson'> {
  constructor() {
    super('ndjson')
  }
  encode(data: any[]) {
    return data.map((row) => JSON.stringify(row)).join('\n')
  }
}
function getOutput<F extends 'csv' | 'ndjson'>(format: F): Output<F> {
  switch (format) {
  case 'csv': return new CSV()
  case 'ndjson': return new NDJSON()
  }
}