Also, in recent versions of Deno (starting with 1.5), we have started to use a Rust library to do transformations of TypeScript to JavaScript in certain scenarios. Because of this, there are certain situations in TypeScript where type information is required, and therefore those are not supported under Deno. If you are using as stand-alone, the setting to use is "isolatedModules" and setting it to true to help ensure that your code can be properly handled by Deno.

One of the ways to deal with the extension and the lack of magical resolution is to use which would allow you to specify “packages” of bare specifiers which then Deno could resolve and load.

Deno is built with a specific version of TypeScript. To find out what this is, type the following on the command line:

We do not consider changes in behavior or breaking changes in TypeScript releases as breaking changes for Deno. TypeScript is a generally mature language and breaking changes in TypeScript are almost always “good things” making code more sound, and it is best that we all keep our code sound. If there is a blocking change in the version of TypeScript and it isn’t suitable to use an older release of Deno until the problem can be resolved, then you should be able to use --no-check to skip type checking all together.

In addition you can utilize @ts-ignore to ignore a specific error in code that you control. You can also replace whole dependencies, using import maps, for situations where a dependency of a dependency isn’t being maintained or has some sort of breaking change you want to bypass while waiting for it to be updated.

As of Deno 1.5 we defaulted to isolatedModules to true and in Deno 1.6 we removed the options to set it back to false via a configuration file. The isolatedModules option forces the TypeScript compiler to check and emit TypeScript as if each module would stand on its own. TypeScript has a few type directed emits in the language at the moment. While not allowing type directed emits into the language was a design goal for TypeScript, it has happened anyways. This means that the TypeScript compiler needs to understand the erasable types in the code to determine what to emit, which when you are trying to make a fully erasable type system on top of JavaScript, that becomes a problem.

So instead of trying to get every user to understand when and how we could support the type directed emits, we made the decision to disable the use of them by forcing the isolatedModules option to true. This means that even when we are using the TypeScript compiler to emit the code, it will follow the same “rules” that the Rust based emitter follows.

This means that certain language features are not supportable. Those features are:

• const enum is not supported. const enums require type information to direct the emit, as s get written out as hard coded values. Especially when const enums get exported, they are a type system only construct.
• export = and import = are legacy TypeScript syntax which we do not support.

While tsc supports language service plugins, Deno does not. Deno does not always use the built in TypeScript compiler to do what it does, and the complexity of adding support for a language service plugin is not feasible. TypeScript does not support emitter plugins, but there are a few community projects which hack emitter plugins into TypeScript. First, we wouldn’t want to support something that TypeScript doesn’t support, plus we do not always use the TypeScript compiler for the emit, which would mean we would need to ensure we supported it in all modes, and the other emitter is written in Rust, meaning that any emitter plugin for TypeScript wouldn’t be available for the Rust emitter.