/*

Description:

Given an array of 4 integers

[a,b,c,d] representing two points (a, b) and (c, d), return a string representation of the slope of the line joining these two points.

For an undefined slope (division by 0), return undefined . Note that the “undefined” is case-sensitive.

a:x1

b:y1

c:x2

d:y2

Assume that [a,b,c,d] and the answer are all integers (no floating numbers!). Slope: https://en.wikipedia.org/wiki/Slope

*/

const slope = ([x1, y1, x2, y2]) => {

const result = (y2 – y1) / (x2 – x1)

return isFinite(result) ? `${result}` : ‘undefined’

}