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'.
2021 update
Akxe's answer suggests ReturnType<Type> technique introduced in Typescript 2.3:
let n: ReturnType<typeof setTimeout>;
n = setTimeout(cb, 500);
It is nice and seems to be preferred over explicit casting. But the result type of "n" in this case is "NodeJS.Timeout", and it is possible to use it as follows:
let n: NodeJS.Timeout;
n = setTimeout(cb, 500);
The only problem with ReturnType/NodeJS.Timeout approach is that numeric operations in browser-specific environment still require casting:
if ((n as unknown as number) % 2 === 0) {
clearTimeout(n);
}
Original answer
A workaround that does not affect variable declaration:
let n: number;
n = setTimeout(function () { /* snip */ }, 500) as unknown as number;
Also, in browser-specific environment it is possible to use window object with no casting:
let n: number;
n = window.setTimeout(function () { /* snip */ }, 500);