Math.abs()

Math.abs(x);

<script language='JavaScript' type='text/JavaScript'>
<!--
document.write(Math.abs(-5)); // output is 5
document.write("<br>");
document.write(Math.abs(5.56)); // output is 5.56
document.write("<br>");
document.write(Math.abs(-2.5)); // output is 2.5
document.write("<br>");
document.write(Math.abs(-1.355)); // output is 1.355
document.write("<br>");
//-->
</script>

document.write(Math.abs(43-64)); // output is 21

Demo of Math.abs function

<script type="text/javascript">
function disp_data(){
var a1 = document.getElementById('t1').value;
a1=Math.abs(a1);
document.getElementById("a2").innerHTML= a1;
}
</script>

<input type=text name=t1 id='t1' value=-12.78><input type=button value='Display rounded number' onClick='disp_data()';> 
<div id='a2'  style=" background-color: #c0f0c0; width:200" > Enter a number</div>