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!