Euler18.js

#!/usr/bin/env node

const s = "75\n" +
          "95 64\n" +
          "17 47 82\n" +
          "18 35 87 10\n" +
          "20 04 82 47 65\n" +
          "19 01 23 75 03 34\n" +
          "88 02 77 73 07 63 67\n" +
          "99 65 04 28 06 16 70 92\n" +
          "41 41 26 56 83 40 80 70 33\n" +
          "41 48 72 33 47 32 37 16 94 29\n" +
          "53 71 44 65 25 43 91 52 97 51 14\n" +
          "70 11 33 28 77 73 17 78 39 68 17 57\n" +
          "91 71 52 38 17 14 91 43 58 50 27 29 48\n" +
          "63 66 04 68 89 53 67 30 73 16 69 87 40 31\n" +
          "04 62 98 27 23 09 70 98 73 93 38 53 60 04 23";

const tri = s.split(/\n/).map(function(line) {
  return line.split(" ").map(Number)
});

function merge(bottom, top) {
  return top.map(function(num,i) {
    return num + Math.max(bottom[i], bottom[i+1]);
  });
}

const r = tri.reverse().reduce(merge)[0];

console.assert(r === 1074, "result is not 1074");
console.log("result", r);