I have a simple TypeScript (ts) which needs a function from a JavaScript file. How can I import that js file into ts file? Do I have to create a ts file for that js file to be able to use it in my ts file?
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2 Answers
The easiest way is to just declare the function you're using:
File1.js
function greet() { return "Hello!"; }
File2.ts
declare function greet(): string;
/* ... later ... */
var hi = greet();
If your scenario is more complex (i.e. multiple files referencing File1.js, or there are many functions in File1.js that would clutter up File2.ts), you can make a File1.d.ts file and reference that from File2.ts:
File1.d.ts
function greet(): string;
File2.ts
/// <reference path="File1.d.ts" />
/* ... later ... */
var hi = greet();
4 Comments
kind_robot
Hi Ryan, thank you this works! One file I use however has methods added to Math library. So Math.uuid.js file has three methods in it; Math.uuid() returns string, and other two... TS complains to this "declare function Math.uuid(): string;" (obviously). How would I bring these methods in? Thanks!
kind_robot
Found it! I declared this interface... interface Math { uuid(): string; } and it's all good.
David Thielen
Is there a way to automatically generate a *.d.ts file from the .js file? Thanks - dave
Simon_Weaver
@DavidThielen some good explanations of why that's not easy to do here typescript.codeplex.com/discussions/451987. i'm sure there's much more written on the subject but this satisfied my questions
Just for the archives,if you add a /// ref for a JavaScript file inside your TS file, the compiler will try to validate all the code in the JS files and throw a huge error list. Try it with jQuery or something like that and you'll see what I mean.
4 Comments
kind_robot
Yup, I have seen that. I put declare var $ and not include that ref in projects which don't have jquery the d.ts file.
Joel Cochran
That's the quickest way to add support for any type that you don't have a .d.ts file for. The nice thing about the definition files is you get Intellisense.
Joel Cochran
I use DefinitelyTyped files all the time, that's a great project.
Simon_Weaver
it doesn't even let you do this (i'm not sure if this changed since 2012) - you get
Incorrect reference: Only files with a .ts extension are allowed - or maybe you meant to rename the .js to .ts. either way you're certainly right that you get a big mess :-)