code does not what you think! Or am I the only one? about wtfjs

[elxris]

You are not writting equivalent code, because in the first you are using the =! operator and store it in num variable. Then you use the ternary operator, and in the false condition of the operator you are using another ternary operator, but, if you are reaching the false side of the first operator you are always running ++n wich is leads something like false + 1 => 0 + 1 => 1.
This is the actual rewrite of the first function:

function okayJS2() {
  let num, num2, els, len, el, el2;
  els = arr;
  len = els.length;
  num = Math.floor(Math.random()*len);
  el = els[num];
  num2 = Math.floor(Math.random()*len);
  num =! num2 // This is an assigment operator and coerces the value to boolean
  if (num) el2 = els[num2]
  else el2 = els[++num] // Wich always is the 1-index wich is the number 2
  console.log(num, num2, el, el2)
}