I'm working on an npm module using TypeScript that includes several interfaces. In the index.ts file, I export all of the classes and interfaces. I defined the interfaces as "interface dto {a:string;} export default dto".
However, when I import the interface in the index.ts file like this: { dto: dto }
The transpilation process seems to remove it.
What is the best way to expose interfaces outside of the npm module?
Once it undergoes transpilation, it disappears.
If an import is not utilized, it gets removed. This intentional behavior ensures that you do not create a runtime dependency on a module if it is only needed for compile-time type analysis.
This concept is also explained here: https://basarat.gitbooks.io/typescript/content/docs/project/external-modules.html#import-type-only
While TypeScript relies heavily on interfaces, they do not directly translate to JavaScript in their native form...
In TypeScript, interfaces are primarily utilized for type safety during the build process. They operate more like a "duck test," where if something behaves like a specific type, then it is treated as such, rather than requiring explicit implementation by classes as seen in other statically-typed languages. Instead of using classes, TypeScript encourages the use of interfaces.
Transpiling involves converting TypeScript code into JavaScript so that it can be executed by traditional JS engines, such as those found in web browsers.
The advantages of TypeScript interfaces are most apparent during the writing and compilation stages of development. Once the code is compiled, these interfaces do not have an equivalent representation in JavaScript and essentially disappear.
Nevertheless, TypeScript offers a method for importing declarations from .d.ts files which serve a similar purpose in conveying type information about the resulting JavaScript code. This allows TypeScript users to maintain strong typing even when interacting with the generated JavaScript.
Although Basarat shared a link to his informative book, I believe that another resource provides a clearer answer to the original question:
https://basarat.gitbooks.io/typescript/docs/types/ambient/d.ts.html
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