How To Make A Sleep Function In TypeScript?

Tim Mouskhelichvili

May 4, 2022 • 2 minutes to read

In TypeScript, there could be many scenarios where a developer might want to pause or sleep a function's execution for a specific time. This function used to be hard to implement, but nowadays, promises make it very simple.

To implement a sleep function in TypeScript, create a helper function and use it when needed.

typescriptconst sleep = (ms) => new Promise(r => setTimeout(r, ms));

console.log('1');
// Sleeps for 2 seconds.
await sleep(2000);
console.log('2');

In this article, I will explain different ways of creating a sleep function in TypeScript and how to implement a sleep function in ES5.

Let's get to it 😎.

Page content

How to implement a sleep function?
Final thoughts

How to implement a sleep function?

With a promise (for ES6)

Implementing a sleep function in ES6 is simple using the async/await keywords, a promise, and a setTimeout.

A promise represents an asynchronous operation and its result after its completion. It represents a proxy for a value that may be known in the future.

The setTimeout is a built-in JavaScript function that calls a callback after a specified number of milliseconds have passed.

Here is a one-line implementation example of the sleep function:

typescriptconst sleep = (ms) => new Promise(r => setTimeout(r, ms));

Note: This implementation of the sleep function accepts milliseconds (1 second = 1000 milliseconds).

Then you can use this helper function in your code when needed:

typescriptconsole.log('1');
// Sleeps for 4 seconds.
await sleep(4000);
console.log('2');

With a callback (for ES5)

Unfortunately, you cannot use the async/await keywords in ES5 because this version of JavaScript doesn't support promises.

However, you can still simulate a sleep function using a callback and a setTimeout.

typescriptvar testSleepES5 = function () {
    console.log('1');
    setTimeout(function () {
        console.log('2');
    }, 4000);
}

testSleepES5();

In this example, we call the second part of the function after a 4 seconds delay.

As you can see, this is less intuitive than using the async/await keywords but still works.

Final thoughts

In conclusion, it is straightforward to implement a sleep helper function using promises. I recommend placing that function inside your utils folder and importing it when needed.

Finally, here are some of my other related tutorials:

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