discriminatedUnions.js

const values = [
  { kind: "Foo", n: 10001 },
  { kind: "Bar", s: "Hello world!" }
];

function match(value, pattern, discriminant = "kind") {
  return pattern[value[discriminant]]?.(value);
}

for (const value of values) {
  match(value, {
    Foo: ({ n }) => {
      console.log(`Encountered a Foo with n: ${n}`);
    },
    Bar: ({ s }) => {
      console.log(`Bar came with a message: ${s}`);
    }
  });
}