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JavaScript Allow Only Numbers?
I am learning a bit on how to code in JavaScript and I just made a basic thing that tells you if the number is prime or not.
Here's the code:
<html>
<body>
<script type="text/javascript">
function calc ()
{
input = document.math_form.user_input.value;
var equ = input / 2
if(equ == Math.round(equ))
{
alert("This number is not prime")
}
else
{
alert("This number is prime")
}
}
</script>
<form name="math_form">
Number:
<input type="text" name="user_input"><br><br>
<input type="button" name="findout" value="Find Out"
onClick="calc ()"><br><br>
Result:
<input type="text" name="result">
</body>
</html>
I was wondering if there is a way to allow only numbers in the input box. Is there some way you can alert the user if it is an invalid number? Thank you
3 Answers
- richarduieLv 61 decade agoFavorite Answer
Your test is not for primality but rather even-ness.
<html>
<head>
<script type="text/javascript">
function calc() {
var input = parseInt( document.math_form.user_input.value );
if (isNaN( input ) {
alert( 'input must be an integer' );
return;
}
var equ = input / 2;
if(equ == Math.round( equ )) {
alert("This number is even")
}
else {
alert("This number is not even")
}
}
</script>
</head>
<body>
<form name="math_form">
Number:
<input type="text" name="user_input" /><br><br>
<input type="button" name="findout" value="Find Out"
onclick="calc()" /><br><br>
Result:
<input type="text" name="result" />
</form>
</body>
</html>
- 1 decade ago
To test for only numbers you would use regular expressions and the test function. For example, a sample number check function would be:
var numRE = /^\d*$/; /* slash d is Regex for numbers only */
function numberCheck(num){
if(numRE.test(num)){
return true;
} else {
return false;
}
}
As far as alerting the user...
The most simple (and annoying) way is when a user leaves the field (onblur) to run the same function above but to alert the user that they need to only enter a number.
var numRE = /^\d*$/; /* slash d is Regex for numbers only */
function numberCheck(num){
if(!numRE.test(num)){
alert('You can only enter a number in this field!');
document.getElementById('user_input').focus();
return false;
}
}
<input type="text" name="user_input" id="user_input" onblur="numberCheck(this.value)">
A better way for the message however, would be to make the field a different color, add a warning icon, and a message saying the same information that would go in an alert. This would be done by using createElement and changing the styles with javascript.
A better way for the javascript itself is to take the events off of the HTML and attach them to an event inside of the Javascript.
See:
- 1 decade ago
Hi!
As far as I am aware (and I may be wrong) it is very difficult to allow only numbers to be entered into a text field. However, the script at the following link will work for validation:
http://wsabstract.com/script/script2/numc.shtml
Important - Whoops! Sorry about that! Didn't thoroughly check through the code to see all the stupid credit notices and rubbish like that. Apologies guys!
I hope this helps!
