TypeScript - use correct version of setTimeout (node vs window)

typescript settimeout
Kevin Tighe picture Kevin Tighe · Aug 21, 2017 · Viewed 69.7k times · Source

I am working on upgrading some old TypeScript code to use the latest compiler version, and I'm having trouble with a call to setTimeout. The code expects to call the browser's setTimeout function which returns a number:

setTimeout(handler: (...args: any[]) => void, timeout: number): number;

However, the compiler is resolving this to the node implementation instead, which returns a NodeJS.Timer:

setTimeout(callback: (...args: any[]) => void, ms: number, ...args: any[]): NodeJS.Timer;

This code does not run in node, but the node typings are getting pulled in as a dependency to something else (not sure what).

How can I instruct the compiler to pick the version of setTimeout that I want?

Here is the code in question:

let n: number;
n = setTimeout(function () { /* snip */  }, 500);

This produces the compiler error:

TS2322: Type 'Timer' is not assignable to type 'number'.

Answer

Akxe picture Akxe · May 21, 2019 
let timer: ReturnType<typeof setTimeout> = setTimeout(() => { ... });

clearTimeout(timer);

By using ReturnType<fn> you are getting independence from platform. You won't be forced to use any nor window.setTimeout which will break if you run the code no nodeJS server (eg. server-side rendered page).

Good news, this is also compatible with Deno!

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