A simple spinner animation with JavaScript and HTML

spinner.js

var a = ["~", "/", "|", "\"];

// - : -
// ~ : ~

var asyncLoop = function(o) {
  var i = -1;

  var loop = function() {
    i++;
    if (i == o.length) {
      o.callback();
      return;
    }
    o.functionToLoop(loop, i);
  }
  loop(); //init
}

var start = setInterval(function() {
  asyncLoop({
    length: 4,
    functionToLoop: function(loop, i) {
      setTimeout(function() {
        document.getElementById("spin").innerHTML = a[i];
        loop();
      }, 75);
    },
    callback : function(){
    }    
  })
}, 300);

Sample usage:
<span id="spin"></span>
Sample css:
#spin { font-size: 5em; font-family: monospace; }
https://jsfiddle.net/schmelzle/puvyuc4z/