<!DOCTYPE html>
<html>
<head>
<title></title>
</head>
<body>
<p onkeyup="obr()" id="ds" contenteditable="true">
var x = 0;</p>
<script>
function obr(){
var text = document.getElementById("ds")
text = text.innerHTML
text = text.replace(/var/gi,"<span style='color:red;'>var</span>")
document.getElementById("ds").innerHTML = text
}
</script>
</body>
</html>