This is the playground for a blog post about source code metaprogramming with TypeScript.

I take the following data as input via JSON:

[
 {
 "name": "A",
 "type": "boolean"
 },
 {
 "name": "B",
 "type": "number"
 },
 {
 "name": "C",
 "type": "string"
 }
]

...and generate the following TypeScript file in three different ways:

interface SomeInterfaceA {
 discriminator: "A";
 type: boolean;
}
interface SomeInterfaceB {
 discriminator: "B";
 type: number;
}
interface SomeInterfaceC {
 discriminator: "C";
 type: string;
}
export type SomeInterface = SomeInterfaceA | SomeInterfaceB | SomeInterfaceC;

The methods to output a TypeScript file include source code generation via:

1. Template literals
2. A template engine
3. A writer library
4. The TypeScript compiler API

Make sure you have the following tools installed and available in the $PATH environment variable:

• node - any recent version (>=14.17) should do, or you can find the exact version in the .tool-versions file for asdf-vm
• npm - that one usually ships with node

Install all dependencies with:

$ npm ci

Either build the project and inspect the output files in ./dist:

$ npm run build

...or execute the generate:*-scripts one-by-one to inspect their output in the console:

# Template literals
$ npm run -s generate:1

# A template engine
$ npm run -s generate:2

# A writer library
$ npm run -s generate:3

# The TypeScript compiler API
$ npm run -s generate:4

Have fun!