Polyfunc.js

A library to create polymorphic functions without the headache of TypeScript unions

You will NEVER have to deal with a mess like this again:

function a(b: number);
function a(b: string);
function a(b: boolean, c: number);
function a(b: SomeClass, c: string, d: boolean);
function a(b: number | string | boolean | SomeClass, c?: number | string, d?: boolean): string {
    if (c == undefined && d == undefined) {
        if (typeof b == "number") return "first thing";
        if (typeof b == "string") return "second thing";
    }
    else if (d == undefined) {
        if (typeof b == "boolean" && typeof c == "number") return "third thing";
    }
    else if (b instanceof SomeClass && typeof c == "string" && typeof d == "boolean") return "fourth thing";

    throw new Error("Invalid arguments given.");
}

That is disgusting. This is absolutely not readable. We need a new solution. Enter polyfunc.js. Here's how you would handle that with the library:

import Poly from "polyfunc";

function a(b: number);
function a(b: string);
function a(b: boolean, c: number);
function a(b: SomeClass, c: string, d: boolean);
function a(b: number | string | boolean | SomeClass, c?: number | string, d?: boolean): string {
    return Poly.match<string>('number').set(() => "first thing")
        .match('string').set(() => "second thing")
        .match('boolean', 'number').set(() => "third thing")
        .match(SomeClass, 'string', 'boolean').set(() => "fourth thing")
        .fallback(() => throw new Exception("Invalid arguments given"))
        .evaluate(...arguments);
}

Yeah, WAY cleaner. Sadly, you still have to do that weird union thing for the function parameters - no matter how clean Polyfunc.js is, it can't change the TypeScript type rules. But, no more of that weird control logic to achieve even basic polymorphism!

And, that's pretty much it. If it wasn't clear from usage, or you need a list of full type validation capabilities, you can see how to use this library in documentation.md.

Install

npm install polyfunc