How to create a fluent chaining equation solver that can work `one().plus().two().equalTo()`

Question

I have been given a task at my internship , I have to create math operations like plus(), minus() etc. using this and new keywords.

example: one().plus().two().equalTo() , given line of code must return 3.

I tried creating functions which returns values.

function one(){
    return 1;
}

But I am not able to figure out how plus() and equalTo() will work.

Answer 1

Here's a solution using function chaining:

const numbering = (fn, n) => () => fn?.(n) ?? n;

function one() {
  this._fn = numbering(this._fn, 1);
  return this;
}

function two() {
  this._fn = numbering(this._fn, 2);
  return this;
}

function plus() {
  const fn = this._fn;
  this._fn = n => (fn?.() ?? 0) + n;
  return this;
}

function equalTo() {
  const fn = this._fn;
  delete this._fn;
  return fn?.() ?? 0;
}


console.log(one().plus().two().equalTo());                // 3
console.log(one().plus().two().plus().two().equalTo());   // 5