JSFiddle - React, Tailwind, and code Playground

JavaScript

function sum_pairs1(arr, sum){
 for(var i=1; i<arr.length;i++){
   for(var n=0;n<i;n++){
    if(arr[n]+arr[i]===sum) return [arr[n], arr[i]];
    }
 }
}

var sum_pairs2=function(ints, s){
  var x, y;
  var end = ints.length;
  for (var j = 0; j < end; j++) {
  var t = s - ints[j]; 
  
    for (var i = j + 1; i < end; i++) {
      if (t == ints[i]) {
        x = j;
        y = i;
        end = i;
      }
    }
  }
  return x == undefined ? x : [ints[x], ints[y]];
}

var a = [...new Array(50000).fill(0).map(_ => Math.round(Math.random()*8)), 14, 16];
var a1 = a.slice();
var a2 = a.slice();

console.time('1');
console.log(sum_pairs1(a1,30))
console.timeEnd('1');

console.time('2');
console.log(sum_pairs2(a2,30))
console.timeEnd('2');