*.d.ts vs *.ts
Written byPhuoc Nguyen
Category
TypeScript
Created
20 Aug, 2020
#Difference
`.ts`
is the standard TypeScript files. The content then will be compiled to JavaScript.`*.d.ts`
is the type definition files that allow to use existing JavaScript code in TypeScript.For example, we have a simple JavaScript function that calculates the sum of two numbers:
// math.js
const sum = (a, b) => a + b;
export { sum };
TypeScript doesn't have any information about the function including the name, the type of parameters. In order to use the function in a TypeScript file, we provide its definition in a
`d.ts`
file:// math.d.ts
declare function sum(a: number, b: number): number;
From now on, we can use the function in TypeScript without any compile errors.
The
`d.ts`
file doesn't contain any implementation, and isn't compiled to JavaScript at all.#Good to know
TypeScript provides an option named
`allowJs`
which allows to use plain JavaScript code in TypeScript.// tsconfig.json
{
"compilerOptions": {
"allowJs": true,
...
}
}
It's very useful when we want to migrate the existing code base from plain JavaScript to TypeScript. So we can convert each JavaScript file to TypeScript one by one without having to convert entire code completely.
See the migrating from JavaScript guide for more information.
Questions? 🙋
Do you have any questions? Not just about this specific post, but about any topic in front-end development that you'd like to learn more about? If so, feel free to send me a message on Twitter or send me an email. You can find them at the bottom of this page.
I have a long list of upcoming posts, but your questions or ideas for the next one will be my top priority. Let's learn together! Sharing knowledge is the best way to grow 🥷.
Recent posts ⚡
Add autocomplete to your text area
28 Sep, 2023
Linear scale of a number between two ranges
28 Sep, 2023
Highlight the current line in a text area
27 Sep, 2023
Create your own custom cursor in a text area
27 Sep, 2023
Mirror a text area for improving user experience
26 Sep, 2023
Display the line numbers in a text area
24 Sep, 2023
Select a given line in a text area
24 Sep, 2023
Highlight keywords in a text area
23 Sep, 2023
Calculate the reading time of a webpage
23 Sep, 2023
createDocumentFragment vs createElement
22 Sep, 2023
Enter full-screen mode
22 Sep, 2023
Newsletter 🔔
If you're into front-end technologies and you want to see more of the content I'm creating, then you might want to consider subscribing to my newsletter.
By subscribing, you'll be the first to know about new articles, products, and exclusive promotions.
Don't worry, I won't spam you. And if you ever change your mind, you can unsubscribe at any time.
Phước Nguyễn