Dot dotdot dotdotdot as loading?

<span id="wait">.</span>

<script>
var dots = window.setInterval( function() {
    var wait = document.getElementById("wait");
    if ( wait.innerHTML.length > 3 ) 
        wait.innerHTML = "";
    else 
        wait.innerHTML += ".";
    }, 100);
</script>

Or you can get fancy and have them go forward and back:

<span id="wait">.</span>

<script>
    window.dotsGoingUp = true;
    var dots = window.setInterval( function() {
        var wait = document.getElementById("wait");
        if ( window.dotsGoingUp ) 
            wait.innerHTML += ".";
        else {
            wait.innerHTML = wait.innerHTML.substring(1, wait.innerHTML.length);
            if ( wait.innerHTML === "")
                window.dotsGoingUp = true;
        }
        if ( wait.innerHTML.length > 9 )
            window.dotsGoingUp = false;



        }, 100);
    </script>

Or you could make them go back and forth randomly:

<span id="wait">.</span>

<script type="text/javascript">
    var dots = window.setInterval( function() {
        var wait = document.getElementById("wait");
        if ( Math.random() < .7 )
            wait.innerHTML += ".";
        else
            wait.innerHTML = wait.innerHTML.substring(1, wait.innerHTML.length);
        }, 100);
</script>

Or I could get a life and stop posting additional snippets.... :D

As Ivo said in the comments, you need to clear the interval at some point, especially if you are not loading a new page after the waiting is finished. :D

Or.. you can do it with CSS ;)

<p class="loading">Loading</p>

.loading:after {
  content: ' .';
  animation: dots 1s steps(5, end) infinite;
}

@keyframes dots {
  0%, 20% {
    color: rgba(0,0,0,0);
    text-shadow:
      .25em 0 0 rgba(0,0,0,0),
      .5em 0 0 rgba(0,0,0,0);}
  40% {
    color: white;
    text-shadow:
      .25em 0 0 rgba(0,0,0,0),
      .5em 0 0 rgba(0,0,0,0);}
  60% {
    text-shadow:
      .25em 0 0 white,
      .5em 0 0 rgba(0,0,0,0);}
  80%, 100% {
    text-shadow:
      .25em 0 0 white,
      .5em 0 0 white;}}

Codepen sample

Example: https://codepen.io/lukaszkups/pen/NQjeVN

You can animate css content too!

// HTML
<p>Loading<span></span></p>

// CSS (nested SASS)
p
  span
    &:before
      animation: dots 2s linear infinite
      content: ''

  @keyframes dots
    0%, 20%
      content: '.'
    40%
      content: '..'
    60%
      content: '...'
    90%, 100%
      content: ''