If I enter value 10 in text area then it will pop up an alert and return square of the entered value but not getting it.
function g() {
var a = document.getElementsById("number").value;
if (a == 10) {
alert(a * a);
return false;
}
}<script type="text/javascript" src="g.js">
</script>
<form onsubmit="return g()">
Enter No:<input type="text" id="number" name="number" /><br/>
<input type="submit" value="c" />
</form>