Multimethod

index.js

function multiMethod() {
  const methodMap = new Map();

  const fn = function (name, ...args) {
    const fn = methodMap.get(name);
    if (typeof fn === 'undefined') {
      throw new TypeError(`Invalid method name "${name}"`);
    }
    return fn(...args);
  };

  fn.def = function (name, fn) {
    if (methodMap.has(name)) {
      throw new TypeError(`Method "${name}" is already defined`);
    }
    methodMap.set(name, fn);
    return this;
  };

  return fn;
}

const calulcator = multiMethod()
  .def('+', (a, b) => a + b)
  .def('-', (a, b) => a - b)
  .def('*', (a, b) => a * b)
  .def('/', (a, b) => a / b);