function DNAtranscribe(strand1) {
  let strand = strand1.split("");
  var newStrand = [];
  for (var i = 0; i < strand.length; i++) {

    if (strand[i] === "A") {
      newStrand.push("U");
    }
    else if (strand[i] === "C") {
      newStrand.push("G");

    }
    else if (strand[i] === "G") {
      newStrand.push("C");
    }
    else if (strand[i] === "T") {
      newStrand.push("A");
    }
    else if (strand[i] !== "A"|| strand[i] !== "C" || strand[i] !== "G" || strand[i] !== "T") {
      return "Invalid Input"
    }

  }
  return newStrand.join("");
}

console.log(DNAtranscribe("ACGXX"));