Typescript how to use type from package

Question

I created an NPM package with a type defined (incl use):

(SolarEdge.js)

export type Period = 'DAY' | 'QUARTER_OF_AN_HOUR' | 'MONTH' | 'HOUR' | 'WEEK' | 'MONTH' | 'YEAR';
public getData = async (site: number, start: string, end: string, period: Period) => {}

(index.js)

export { default } from './SolarEdge';

After compiling from ts, I get 4 files (index.js, index.d.ts, SolarEdge.js, SolarEdge.d.ts)

When using this from my express app, it is complaining that I cant pass a string to this function, because it wants a Period.

Error: Argument of type 'string' is not assignable to parameter of type 'Period'.ts(2345)

Code:

    const data = await solaredge.getData(
        parseInt(req.params.site),
        req.params.start,
        req.params.end,
        //'MONTH',
        req.params.period,
    );

req.params.period contains a string with 'MONTH' or something else. WHen using the hardcoded string MONTH it works, but using the req.params.period variable, it doesnt.

I tried doing: req.params.period as Period but the problem is: it cant find Period.

How does this work?

Maybe the period is accessible via solaredge.Period, assuming that the type is being exported? — Terry
– Terry, Commented Dec 28, 2019 at 11:21
I created this package myself, so Im just curious how I should do that. SolarEdge.Period doesnt work. Ill add my package code in the question — Eric Jansen
– Eric Jansen, Commented Dec 28, 2019 at 12:26

jmellman · Accepted Answer · 2019-12-28 19:45:40Z

1

TypeScript libraries that want to support TypeScript consumers must explicitly export their types as well as emit declaration files during compilation.

It looks like you're already doing this, so you should be able to explicitly import the Period type for use in your application code:

import { getData, Period }  from 'solaredge'

...

const data = await solaredge.getData(
    parseInt(req.params.site),
    req.params.start,
    req.params.end,
    //'MONTH',
    req.params.period as Period,
);

answered Dec 28, 2019 at 19:45

jmellman

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1 Comment

Eric Jansen Over a year ago

This is the answer I had to explicitly export the type and then explicitly import in my code

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