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

TypeScript - Use the Correct Version of setTimeout (Node vs. Window) ⏱️🖥️

Are you working on upgrading some old TypeScript code and running into trouble with a call to setTimeout? 🚧😫

In TypeScript, the setTimeout function can have different typings depending on whether you are running in a browser environment (window) or a Node.js environment. 🌐🐦

Let's take a closer look at the issue and explore easy solutions to instruct the TypeScript compiler to pick the version of setTimeout that you want! 🕵️‍♀️🔍

The Problem 🤔❓

When using setTimeout in TypeScript, the compiler may incorrectly resolve the function to the Node.js implementation, even if you are working in a browser environment. This can lead to compiler errors and unexpected behavior. 😱🔀

The incorrect resolution results in the setTimeout function returning a NodeJS.Timer type instead of the expected number type. As a result, you might encounter a compiler error similar to:

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

So how do we fix this issue and ensure that the correct version of setTimeout is used? Let's dive into the solutions! 💡💪

Solution 1: Specify the Environment 🌍🔧

One way to address this problem is by specifying the environment explicitly to the TypeScript compiler. You can define a custom global variable that tells the compiler you are working in a browser environment. Simply add the following line to your TypeScript file:

declare const window: Window;

This declaration tells the compiler that there is a global variable named window of type Window, which represents the browser environment. It helps the compiler accurately resolve the typings for browser-specific functions like setTimeout. 🌐📝

Solution 2: Type Assertion ✅🔍

Another approach is to use a type assertion to explicitly specify the type of the setTimeout result. By casting the result to number, you inform the compiler that even though the Node.js typings may be present, you specifically want the return type to be a number. Here's how you can do it:

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

The as number syntax performs the type assertion, overriding the default NodeJS.Timer type with the desired number type. Now, the compiler error should disappear, and your code should work as expected! ✅🌈

Call to Action ✍️🎉

Now that we have explored easy solutions to resolve the issue of using the correct version of setTimeout in TypeScript, it's time for you to implement these solutions and keep your code running smoothly! 🚀🤓

Try out the solutions presented in this blog post, and let us know how they worked for you! If you have any questions or alternative solutions, feel free to share them in the comments section below. Let's keep the conversation going! 💬🗯️

Happy coding! 👩‍💻👨‍💻