denoland-deno/docs/runtime/compiler_apis.md

Compiler API

Deno supports runtime access to the built-in TypeScript compiler. There are three methods in the Deno namespace that provide this access.

Deno.compile()

This works similar to deno cache in that it can fetch and cache the code, compile it, but not run it. It takes up to three arguments, the rootName, optionally sources, and optionally options. The rootName is the root module which will be used to generate the resulting program. This is like the module name you would pass on the command line in deno run --reload example.ts. The sources is a hash where the key is the fully qualified module name, and the value is the text source of the module. If sources is passed, Deno will resolve all the modules from within that hash and not attempt to resolve them outside of Deno. If sources are not provided, Deno will resolve modules as if the root module had been passed on the command line. Deno will also cache any of these resources. The options argument is a set of options of type Deno.CompilerOptions, which is a subset of the TypeScript compiler options containing the ones supported by Deno.

The method resolves with a tuple. The first argument contains any diagnostics (syntax or type errors) related to the code. The second argument is a map where the keys are the output filenames and the values are the content.

An example of providing sources:

const [diagnostics, emitMap] = await Deno.compile("/foo.ts", {
  "/foo.ts": `import * as bar from "./bar.ts";\nconsole.log(bar);\n`,
  "/bar.ts": `export const bar = "bar";\n`,
});

assert(diagnostics == null); // ensuring no diagnostics are returned
console.log(emitMap);

We would expect map to contain 4 "files", named /foo.js.map, /foo.js, /bar.js.map, and /bar.js.

When not supplying resources, you can use local or remote modules, just like you could do on the command line. So you could do something like this:

const [diagnostics, emitMap] = await Deno.compile(
  "https://deno.land/std/examples/welcome.ts"
);

In this case emitMap will contain a simple console.log() statement.

Deno.bundle()

This works a lot like deno bundle does on the command line. It is also like Deno.compile(), except instead of returning a map of files, it returns a single string, which is a self-contained JavaScript ES module which will include all of the code that was provided or resolved as well as exports of all the exports of the root module that was provided. It takes up to three arguments, the rootName, optionally sources, and optionally options. The rootName is the root module which will be used to generate the resulting program. This is like module name you would pass on the command line in deno bundle example.ts. The sources is a hash where the key is the fully qualified module name, and the value is the text source of the module. If sources is passed, Deno will resolve all the modules from within that hash and not attempt to resolve them outside of Deno. If sources are not provided, Deno will resolve modules as if the root module had been passed on the command line. Deno will also cache any of these resources. The options argument is a set of options of type Deno.CompilerOptions, which is a subset of the TypeScript compiler options containing the ones supported by Deno.

An example of providing sources:

const [diagnostics, emit] = await Deno.bundle("/foo.ts", {
  "/foo.ts": `import * as bar from "./bar.ts";\nconsole.log(bar);\n`,
  "/bar.ts": `export const bar = "bar";\n`,
});

assert(diagnostics == null); // ensuring no diagnostics are returned
console.log(emit);

We would expect emit to be the text for an ES module, which would contain the output sources for both modules.

When not supplying resources, you can use local or remote modules, just like you could do on the command line. So you could do something like this:

const [diagnostics, emit] = await Deno.bundle(
  "https://deno.land/std/http/server.ts"
);

In this case emit will be a self contained JavaScript ES module with all of its dependencies resolved and exporting the same exports as the source module.

Deno.transpileOnly()

This is based off of the TypeScript function transpileModule(). All this does is "erase" any types from the modules and emit JavaScript. There is no type checking and no resolution of dependencies. It accepts up to two arguments, the first is a hash where the key is the module name and the value is the content. The only purpose of the module name is when putting information into a source map, of what the source file name was. The second argument contains optional options of the type Deno.CompilerOptions. The function resolves with a map where the key is the source module name supplied, and the value is an object with a property of source and optionally map. The first is the output contents of the module. The map property is the source map. Source maps are provided by default, but can be turned off via the options argument.

An example:

const result = await Deno.transpileOnly({
  "/foo.ts": `enum Foo { Foo, Bar, Baz };\n`,
});

console.log(result["/foo.ts"].source);
console.log(result["/foo.ts"].map);

We would expect the enum would be rewritten to an IIFE which constructs the enumerable, and the map to be defined.

Referencing TypeScript library files

When you use deno run, or other Deno commands which type check TypeScript, that code is evaluated against custom libraries which describe the environment that Deno supports. By default, the compiler runtime APIs which type check TypeScript also use these libraries (Deno.compile() and Deno.bundle()).

But if you want to compile or bundle TypeScript for some other runtime, you may want to override the default libraries. To do this, the runtime APIs support the lib property in the compiler options. For example, if you had TypeScript code that is destined for the browser, you would want to use the TypeScript "dom" library:

const [errors, emitted] = await Deno.compile(
  "main.ts",
  {
    "main.ts": `document.getElementById("foo");\n`,
  },
  {
    lib: ["dom", "esnext"],
  }
);

For a list of all the libraries that TypeScript supports, see the lib compiler option documentation.

Don't forget to include the JavaScript library

Just like tsc, when you supply a lib compiler option, it overrides the default ones, which means that the basic JavaScript library won't be included and you should include the one that best represents your target runtime (e.g. es5, es2015, es2016, es2017, es2018, es2019, es2020 or esnext).

Including the Deno namespace

In addition to the libraries that are provided by TypeScript, there are four libraries that are built into Deno that can be referenced:

• deno.ns - Provides the Deno namespace.
• deno.shared_globals - Provides global interfaces and variables which Deno supports at runtime that are then exposed by the final runtime library.
• deno.window - Exposes the global variables plus the Deno namespace that are available in the Deno main worker and is the default for the runtime compiler APIs.
• deno.worker - Exposes the global variables that are available in workers under Deno.

So to add the Deno namespace to a compilation, you would include the deno.ns lib in the array. For example:

const [errors, emitted] = await Deno.compile(
  "main.ts",
  {
    "main.ts": `document.getElementById("foo");\n`,
  },
  {
    lib: ["dom", "esnext", "deno.ns"],
  }
);

Note that the Deno namespace expects a runtime environment that is at least ES2018 or later. This means if you use a lib "lower" than ES2018 you will get errors logged as part of the compilation.

Using the triple slash reference

You do not have to specify the lib in the compiler options. Deno also supports the triple-slash reference to a lib. which can be embedded in the contents of the file. For example, if you have a main.ts like:

/// <reference lib="dom" />

document.getElementById("foo");

It would compile without errors like this:

const [errors, emitted] = await Deno.compile("./main.ts", undefined, {
  lib: ["esnext"],
});

Note that the dom library conflicts with some of the default globals that are defined in the default type library for Deno. To avoid this, you need to specify a lib option in the compiler options to the runtime compiler APIs.