Variable length currying in JavaScript

object-type-casting.js

const myStrObject = {
  toString: function() {
    return 'Str';
  }
};
console.log('My object is ' + myStrObject); // 'My object is Str'
console.log(myStrObject + 297);             // 'Str297'

const myNumObject = {
  valueOf: function() {
    return 123;
  }
};
console.log('My object is ' + myNumObject); // 'My object is 123'
console.log(myNumObject + 297);             // 420