How to generate random number and use it for action?

My main idea is generating some kind of "random greetings" and the idea is to generate a random number, and depends on the number to display "random greeting". Here is my non working code:

<p id="greeting">Nice to meet you!</p>
<script>
var x = Math.floor((Math.random() * 4) + 1);
if (x == 1) {
  document.getElementById("greeting").innerHTML = "Greeting 1";
} else if (x == 2) {
  document.getElementById("greeting").innerHTML = "Greeting 2";
} else if (x == 3) {
  document.getElementById("greeting").innerHTML = "Greeting 3";
} else if (x == 4) {
  document.getElementById("greeting").innerHTML = "Greeting 4";
}
</script>

I have no idea what's wrong in it, please help!