singledispatch.js - single dispatch generic function like Python's singledispatch

singledispatch.js

// Create a Python singledispatch / Clojure multimethod style function that
// dispatches on the first argument.
//
// Returns a wrapped function that calls appropriate underlying function
// based on prototype of first argument.
//
// Custom implementations for specific types can be registered through calling
// `.define(constructor, fun)` on the wrapped function.
export const singledispatch = fallback => {
  let _key = Symbol('singledispatch method')

  // Assign fallback to Object prototype.
  // This makes it the method of last resort.
  Object.prototype[_key] = fallback

  const dispatch = (object, ...rest) => {
    let method = object[_key]
    return method(object, ...rest)
  }

  dispatch.define = (constructor, method) => {
    constructor.prototype[_key] = method
  }

  return dispatch
}

export default singledispatch

Surprisingly fast in Chrome and Safari... In the same ballpark as plain function call, or method dispatch https://jsperf.app/sanega