Creating Typescript definition files from module.exports = js files

Question

I am trying to create a Typescript definition file for format-duration:

module.exports = (ms) => {
  let { days, hours, minutes, seconds } = parseMs(ms)
  seconds = addZero(seconds)
  if (days) return `${days}:${addZero(hours)}:${addZero(minutes)}:${seconds}`
  if (hours) return `${hours}:${addZero(minutes)}:${seconds}`
  return `${minutes}:${seconds}`
}

I have tried a few different declaration files:

export default function (ms: number): string;

export default function formatDuration(ms: number): string;

export function formatDuration(ms: number): string;

and whilst I do get the correct type information from them when I run the application I get an error:

import formatDuration from "format-duration";

const formatted = formatDuration(123456);

Exception has occurred: TypeError TypeError: format_duration_1.default is not a function

How do I properly define types for this sort of javascript library?

Which one of the export statements give you the half output? — Aakash Verma
– Aakash Verma, Commented Nov 29, 2017 at 21:19
I don't know if it's possible to type a nameless export? In the other cases you should be able to use declare formatDuration:(ms:number):string — Kokodoko
– Kokodoko, Commented Nov 29, 2017 at 21:36
You should read this first -typescriptlang.org/docs/handbook/modules.html#import — user8928802
– user8928802, Commented Nov 29, 2017 at 22:09

Roaders · Accepted Answer · 2017-12-01 18:30:21Z

1

It seems that the correct declaration file looks like this:

declare function formatDuration(ms: number): string;

export = formatDuration;

and it is imported like this:

import formatDuration = require("format-duration");

answered Dec 1, 2017 at 18:30

Roaders

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