What's the Return Type for setTimeout() in Typescript

# The Return Type for setTimeout() in Typescript

Use the ReturnType utility type to get the return type of the setTimeout method.

The ReturnType utility type constructs a type that consists of the function's return type.

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const timeout: ReturnType<typeof setTimeout> = setTimeout(() => {
  console.log('success');
}, 1500);

console.log(timeout);

The ReturnType utility type allows us to construct a type that consists of the return type of the passed-in function.

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function sum(a: number, b: number) {
  return a + b;
}

// 👇️ type T = number
type T = ReturnType<typeof sum>;

This approach is needed because the return type of the setTimeout method is NodeJS.Timeout in Node and number in the browser.

Even though the return type of the setTimeout method is different between Node.js and the browser, the return value is used in the same way.

It is passed to the clearTimeout() method to cancel the timeout if necessary.

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const timeout: ReturnType<typeof setTimeout> = setTimeout(() => {
  console.log('success');
}, 1500);

clearTimeout(timeout);

The clearTimeout method takes a number or a NodeJS.Timeout object as a parameter (depending on the environment), so you can directly pass the timeout value to the method.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• Declare a function with a Promise return type in TypeScript
• How to Declare a Function that throws an Error in TypeScript
• Declare a Function with variable Number of Arguments in TS