JSFiddle - React, Tailwind, and code Playground

JavaScript

var sum_pairs=function(ints, s){
console.time('mark')
  var x, y;
  var end = ints.length;
  for (var j = 0; j < end; j++) {
    for (var i = j + 1; i < end; i++) {
      if (ints[j] + ints[i] == s) {
        x = ints[j];
        y = ints[i];
        end = i;
      }
    }
  }
	console.timeEnd('mark') 
  return x == undefined ? x : [x, y];
}

var x = Array.from({length: 10000000}, () => Math.floor(Math.random() * 100));
sum_pairs(x, 50);