While working on a TypeScript project, I had to save a reference to the setTimeout
function. That’s when I needed to know the return type of the setTimeout
function in JavaScript. There are three different ways to get the return type of the setTimeout
and setInterval
functions in JavaScript.
:number
Using Normally, the return type of the above functions is just a number. This number is the ID of the timer that can be used to clear the timer using the clearTimeout
or clearInterval
functions.
NodeJS.Timeout
Using The first thing GitHub Copilot suggested to me was to use the NodeJS.Timeout
type. This type is provided by the @types/node
package and is a more specific type for the return value of the setTimeout
function.
However, I’m not sure if this type is available in the browser environment and whether it is a number or a node-specific type.
So, here’s the most generic way to get the return type of the setTimeout
function.
ReturnType<typeof setTimeout>
Using The ReturnType
utility type, provided by TypeScript, extracts the return type of a function. We can use this utility type to get the return type of the setTimeout
function.
This way, we can get the return type of the setTimeout
function in JavaScript, no matter if we are working in a Node.js environment or a browser environment.
Conclusion
Even though there are multiple ways to get the return type of the above functions, I recommend using the ReturnType<typeof setTimeout>
method as it is the most generic way.