You must use a .ts file - e.g. test.ts to get Typescript validation, intellisense typing of vars, return types, as well as "typed" error checking (e.g. passing a string to a method that expects an number param will error out).
It will be transpiled into (standard) .js via tsc.
Clarification needed based on down-votes, very helpful comments and other answers.
types
Yes, you can do type checking in VS Code in .js files with @ts-check - as shown in the animation
What I originally was referring to for Typescript types is something like this in .ts which isn't quite the same thing:
hello-world.ts
function hello(str: string): string {
return 1;
}
function foo(str:string):void{
console.log(str);
}
This will not compile. Error: Type "1" is not assignable to String
if you tried this syntax in a Javascript hello-world.js file:
//@ts-check
function hello(str: string): string {
return 1;
}
function foo(str:string):void{
console.log(str);
}
The error message referenced by OP is shown: [js] 'types' can only be used in a .ts file
If there's something I missed that covers this as well as the OP's context, please add. Let's all learn.