ts-macros is a custom typescript transformer which allows you to create function macros. This library is heavily inspired by Rust's macro_rules! macro, and it's just as powerful!

All macro names must start with a dollar sign ($) and must be declared using the function keyword. Macros can then be called just like a normal function, but with a ! after it's name: $macro!(params).

function $contains<T>(value: T, ...possible: Array<T>) {
    // repetition which goes over all the elements in the "possible" array
    return +["||", [possible], (item: T) => value === item];
}

const searchItem = "google";
console.log($contains!(searchItem, "erwin", "tj")); 
// Transpiles to: console.log(false);

Macros can also be chained with any javascript expression.

declare global {
    interface String {
        $contains<T>(...possible: Array<T>) : boolean;
    }
}

"feud".$contains!("google", "feud", "erwin");
// Transpiles to: true

To read more about ts-macros features, visit the documentation, or you can check out the interactive playground if you want to play with macros without having to set up an enviourment!

What you can do with ts-macros:

• Generate repetitive code
• Generate code conditionally, based on enviourment variables or other configuration files
• Create abstractions without the runtime cost

What you can't do with ts-macros:

• Generate types which you can use in your code. ts-macros is only a transformer, it's ran after typechecking, so generating different types has no effect. However, the code inside the macro itself still gets typechecked

npm i --save-dev ts-macros

By default, typescript doesn't allow you to add custom transformers, so you must use a tool which adds them. ttypescript does just that! Make sure to install it:

npm i --save-dev ttypescript

and add the ts-macros transformer to your tsconfig.json:

"compilerOptions": {
    //... other options
    "plugins": [
        { "transform": "ts-macros" }
    ]
}

then transpile your code with ttsc.

const TsMacros = require("ts-macros").default;

options: {
    getCustomTransformers: (program) => ({
        before: [TsMacros(program)]
    }),
}