JSFiddle - React, Tailwind, and code Playground

HTML

<div id='out'>

</div>

JavaScript

const a = { x: 0, y: 0}
const b = { x: 3, y: 3}

function pathNr(A, B) {
	if (A.x === B.x) {
  	return 0
  }
	if (A.x === B.x && A.y === B.y) {
  	return 1;
  }
	return pathNr({A.x, A.y + 1}, B) + pathNr({A.x + 1, A.y}, B)
}

document.getElementById('out').innerHTML = pathNr(a, b)