https://leetcode.com/problems/minimum-window-substring

shortestWindow.js

let S = "ADOBECODEBANC";
let T = "ABC";

let cursors = {};

// init cursors
for (let t of T) cursors[t] = -1;

// O(n) time complexity
S.split('').forEach((s, i) => {
  if (s in cursors && i >= cursors[s])
    cursors[s] = i;
});

// grab all values
let indices = Object.values(cursors);

// present window
let w = {
  s: Math.min.apply(null, indices),
  e: Math.max.apply(null, indices)
};

const valueInWindow = S.slice(w.s, w.e+1);

console.log(valueInWindow);