EcmaScript ToPrimitive internal operation pseudo-code

js-to-primitive-internal.js

function ToPrimitive(input, preferredType){
  
  switch (preferredType){
    case Number:
      return toNumber(input);
      break;
    case String:
      return toString(input);
      break
    default:
      return toNumber(input);  
  }
  
  function isPrimitive(value){
    return value !== Object(value);
  }

  function toString(){
    if (isPrimitive(input.toString())) return input.toString();
    if (isPrimitive(input.valueOf())) return input.valueOf();
    throw new TypeError();
  }

  function toNumber(){
    if (isPrimitive(input.valueOf())) return input.valueOf();
    if (isPrimitive(input.toString())) return input.toString();
    throw new TypeError();
  }
}