Develop Reference

Validate key input in field with javascript

I am using
document.getElementById('input-field').addEventListener('keyup', function (e) {
if (!String.fromCharCode(e.which).match(/[A-Za-z0-9,]/)) {
event.preventDefault();
}
});
It almost works. The problem is that I cannot use key arrows, backspace, delete, ctrl+a, etc.
How can I limit it to only those keys that will give a string representation in the specific input?

To ignore those keys you need to add a condition before validating your input.
For example you can make an array containing the list of all KeyCodes that you want to ignore and just test if the typed key isn't one of them.
Here's what you need:
document.getElementById('input-field').addEventListener('keypress', function(e) {
//An array of special Keys
var specialKeys = [37, 38, 39, 40, 8, 13, 27, 46];
if (specialKeys.indexOf(e.which) === -1) {
console.log(String.fromCharCode(e.which)+ ' Key is validated!');
if (!String.fromCharCode(e.which).match(/[A-Za-z0-9,]/)) {
event.preventDefault();
}
}
});
<input type="text" id="input-field" placeholder="input text here">
Note:
As mentioned in comments you need to use keypressevent instead of keyup to validate every inputted character immediately.

Well there is somehow to limit your input range. But I think in this case you are looking for a way to identify only printable key events.
You can achieve this by using the solution proposed by #TimDown on How to detect if the pressed key will produce a character inside an <input> text-box? applied to a keypress event as you can see on the code below. So then, you can work just with printable key events.
function isCharacterKeyPress(evt) {
if (typeof evt.which == "undefined") {
// This is IE, which only fires keypress events for printable keys
return true;
} else if (typeof evt.which == "number" && evt.which > 0) {
// In other browsers except old versions of WebKit, evt.which is
// only greater than zero if the keypress is a printable key.
// We need to filter out backspace and ctrl/alt/meta key combinations
return !evt.ctrlKey && !evt.metaKey && !evt.altKey && evt.which != 8;
}
return false;
}
document.getElementById('input-field').addEventListener('keypress', function (e) {
if(isCharacterKeyPress(e)){
if (!String.fromCharCode(e.which).match(/[A-Za-z0-9,]/)) {
e.preventDefault();
}
}
});
<input type="text" id="input-field" placeholder="input text here">

How to replace code to use RegExp

I have the following code which checks for "enter" key as well as prevent the use of > and < sign in the textbox.
<script type="text/javascript" language="javascript">
function checkKeycode(e) {
var keycode;
if (window.event) // IE
keycode = e.keyCode;
else if (e.which) // Netscape/Firefox/Opera
keycode = e.which;
if (keycode == 13) {
//Get the button the user wants to have clicked
var btn = document.getElementById(btnSearch);
if (btn != null) { //If we find the button click it
btn.click();
event.keyCode = 0
}
//Removed when above code was added 12-09-13
//CallSearch();
}
}
function CallSearch() {
var objsearchText = window.document.getElementById('txtSearchText');
var searchText;
if ((objsearchText!=null))
{
searchText = objsearchText.value;
searchText = searchText.replace(/>/gi, " >");
searchText = searchText.replace(/</gi, "< ");
objsearchText.value = searchText;
}
//This cookie is used for the backbutton to work in search on postback
//This cookie must be cleared to prevent old search results from displayed
document.cookie='postbackcookie=';
document.location.href="search_results.aspx?searchtext=";
}
</script>
How can I shorten the code to be more effecient and use the onBlur function and to use RegExp instead of replace? Or is replace a faster method than RegExp?

You are saying that you want to prevent < and > chars. Here is an easier way, just ignore these chars when the keydown event occurs on them.
Also I suggest to use jQuery - if you can.
http://api.jquery.com/event.which/
var ignoredChars = [188, 190]; // <, >
$('#myTextField').keydown(function(e) {
if(ignoredChars.indexOf(e.which) > -1) {
e.preventDefault();
e.stopPropagation();
return false;
}
})
.keyup(function(e) {
if(e.which === 13) {
$('#searchButton').click();
}
});
Just add this event handler to your textbox and remove the regexp replacements.
If you don't want characters to be input by user, surpress them as early as possible. This way you won't get in trouble fiddling them out of a big string later.

Line break on keydown

I have a textarea, and on each enter i want it to get blank if something has written. but my problem is; on the first enter it line breaks, and you continue to write from the second line. it only happens at the first enter. there is no problem with emptying the textarea, you just continue to write from the second line, which is the problem.
onkeydown= if(event.keyCode == 13){
sendMessage();
}
function sendMessage(user){
var message = $('#textarea').val();
$('#textarea').val('');
}

if(event.keyCode == 13) {
sendMessage();
if (event.preventDefault) event.preventDefault();
return false;
}
keydown happens before the character is entered in the textarea, so you just have to call preventDefault on the event so it doesn't enter a line break after you've called your function that clears the text-area. return false alone should be enough too if the code above is inline in the HTML, which isn't really recommended. See updated solution below:
For unobtrusiveness and back-compat, I'd recommend doing it all with jQuery:
$('#textarea_ID').keydown(function(e) {
if (e.which == 13) {
e.preventDefault();
var message = $(this).val();
$(this).val('');
//rest of your function using `message` here
}
});
Fiddle

In jQuery use the which property for the code. Then return false with e.preventDefault();
var field = $('.classname');
field.keydown(function(e){
if(e.which==13){
sendMessage();
e.preventDefault();
}
});

Simply add return false; to your keydown function. This prevents the default action of the key (a newline in this case) from being executed.
You may also want to include code to handle Internet Explorer's way of getting keycodes. Your new function would be:
onkeydown = function (e) {
// Gets keycode cross browser
e = window.event ? window.event : e;
var keycode = e.keyCode !== null ? e.keyCode : e.charCode;
// Checks if it was the enter key that was pressed (enter = keycode 13)
if (keycode === 13) {
// Calls function to do stuff
sendMessage();
// Cancels the default action of the (enter) key
return false;
}
}

Focus the next input with down arrow key (as with the tab key)

I have a huge entry form and fields for the users to input.
In the form user use tab key to move to next feild,there are some hidden fields and readonly textboxes in between on which tab key is disabled using javascript.
Now users finds difficult to use tab key and wants same functionality on down arrow key of the keyboard.
I was using the below code to invoke the tab key code on js but not working,please some body help me on this.
function handleKeyDownEvent(eventRef)
{
var charCode = (window.event) ? eventRef.keyCode : eventRef.which;
//alert(charCode);
// Arrow keys (37:left, 38:up, 39:right, 40:down)...
if ( (charCode == 40) )
{
if ( window.event )
window.event.keyCode = 9;
else
event.which = 9;
return false;
}
return true;
}
<input type="text" onkeydown=" return handleKeyDownEvent(event);" >

Using jQuery, you can do this :
$('input, select').keydown(function(e) {
if (e.keyCode==40) {
$(this).next('input, select').focus();
}
});
When you press the down arrow key (keyCode 40), the next input receives the focus.
DEMO​
EDIT :
In Vanilla JS, this could be done like this :
function doThing(inputs) {
for (var i=0; i<inputs.length; i++) {
inputs[i].onkeydown = function(e) {
if (e.keyCode==40) {
var node = this.nextSibling;
while (node) {
console.log(node.tagName);
if (node.tagName=='INPUT' || node.tagName=='SELECT') {
node.focus();
break;
}
node = node.nextSibling;
}
}
};
};
}
doThing(document.getElementsByTagName('input'));
doThing(document.getElementsByTagName('select'));
Note that you'd probably want to map the up key too, and go to first input at last one, etc. I let you handle the details depending on your exact requirements.

This is my final working code:
$('input[type="text"],textarea').keydown( function(e) {
var key = e.charCode ? e.charCode : e.keyCode ? e.keyCode : 0;
if(key == 40) {
e.preventDefault();
var inputs = $(this).parents('form').find(':input[type="text"]:enabled:visible:not("disabled"),textarea');
inputs.eq( inputs.index(this)+ 1 ).focus();
inputs.eq( inputs.index(this)+ 1 ).click();
}
});

If I understand correctly, some fields are read-only, so the tab key still activates them, even though they are read-only, and this is annoying, as you have to press the tab key perhaps several times to get to the next editable field. If that is correct, then an alternate solution would be to use the tabindex attribute on your input fields, indexing each one so that the read-only and otherwise non-editable fields aren't selected. You can find more info on the tabindex attribute here.

Best way to restrict a text field to numbers only?

I'm using the following Javascript to restrict a text field on my website to only accept numerical input, and no other letters or characters. The problem is, it REALLY rejects all other key inputs, like ctrl-A to select the text, or even any other browser functions like ctrl-T or ctrl-W while the text box is selected. Does anyone know of a better script to only allow numerical input, but not block normal commands (that aren't being directly input into the field)? Thanks
Here is the code I'm using now:
function numbersonly(e, decimal)
{
var key;
var keychar;
if (window.event)
key = window.event.keyCode;
else if (e)
key = e.which;
else
return true;
keychar = String.fromCharCode(key);
if ((key==null) || (key==0) || (key==8) || (key==9) || (key==13) || (key==27))
return true;
else if ((("0123456789").indexOf(keychar) > -1))
return true;
else if (decimal && (keychar == "."))
return true;
else
return false;
}
Edit: None of the solutions provided have solved my problem of allowing commands like ctrl-A while the text box is selected. That was the whole point of my asking here, so I have gone back to using my original script. Oh well.

This is something I made another time for just numbers, it will allow all the formatters as well.
jQuery
$('input').keypress(function(e) {
var a = [];
var k = e.which;
for (i = 48; i < 58; i++)
a.push(i);
if (!(a.indexOf(k)>=0))
e.preventDefault();
});​
Try it
http://jsfiddle.net/zpg8k/
As a note, you'll want to filter on submit/server side as well, for sake of pasting/context menu and browsers that don't support the paste event.
Edit to elaborate on multiple methods
I see you're bouncing around the 'accepted' answer, so I'll clear something up. You can really use any of the methods listed here, they all work. What I'd personally do is use mine for live client side filtering, and then on submit and server side use RegEx as suggested by others. However, no client side by itself will be 100% effective as there is nothing stopping me from putting document.getElementById('theInput').value = 'Hey, letters.';
in the console and bypassing any clientside verification (except for polling, but I could just cancel the setInterval from the console as well). Use whichever client side solution you like, but be sure you implement something on submit and server side as well.
Edit 2 - #Tim Down
Alright, per the comments I had to adjust two things I didn't think of. First, keypress instead of keydown, which has been updated, but the lack of indexOf in IE (seriously Microsoft!?) breaks the example above as well. Here's an alternative
$('input').keypress(function(e) {
var a = [];
var k = e.which;
for (i = 48; i < 58; i++)
a.push(i);
if (!($.inArray(k,a)>=0))
e.preventDefault();
});​
New jsfiddle: http://jsfiddle.net/umNuB/

This works in IE, Chrome AND Firefox:
<input type="text" onkeypress="return event.charCode === 0 || /\d/.test(String.fromCharCode(event.charCode));" />

.keypress(function(e)
{
var key_codes = [48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 0, 8];
if (!($.inArray(e.which, key_codes) >= 0)) {
e.preventDefault();
}
});
You need Backspace and Delete keys too ;)

http://jsfiddle.net/PgHFp/
<html>
<head>
<title>Test</title>
<script language="javascript">
function checkInput(ob) {
var invalidChars = /[^0-9]/gi
if(invalidChars.test(ob.value)) {
ob.value = ob.value.replace(invalidChars,"");
}
}
</script>
</head>
<body>
<input type="text" onkeyup="checkInput(this)"/>
</body>
</html>

Just use regex to get rid of any non number characters whenever a key is pressed or the textbox loses focus.
var numInput;
window.onload = function () {
numInput = document.getElementById('numonly');
numInput.onkeydown = numInput.onblur = numInput.onkeyup = function()
{
numInput.value = numInput.value.replace(/[^0-9]+/,"");
}
}

The only event that contains information about the character typed is keypress. Anything character-related you may infer from the keyCode property of keydown or keyup events is unreliable and dependent on a particular keyboard mapping. The following will prevent non-numeric keyboard input all major browsers by using the character obtained from the keypress event. It won't prevent the user from pasting or dragging non-numeric text in.
var input = document.getElementById("your_input");
input.onkeypress = function(evt) {
evt = evt || window.event;
if (!evt.ctrlKey && !evt.metaKey && !evt.altKey) {
var charCode = (typeof evt.which == "undefined") ? evt.keyCode : evt.which;
if (charCode && !/\d/.test(String.fromCharCode(charCode))) {
return false;
}
}
};

I use this:
oEl.keypress(function(ev)
{
var sKey = String.fromCharCode(ev.which);
if (!sKey.match(/[0-9]/) || !sKey === "")
ev.preventDefault();
});
The advantage is, that every key which does not provide an input to the field is still allowed, so you don't have to worry about every single special key. Even combos like CTRL + R do still work.
EDIT
As this is not working in Firefox I had to modify the function a little:
oEl.keypress(function(ev)
{
var iKeyCode = ev.which || ev.keyCode;
var aSpecialKeysForFirefox = [8, 9, 13, 27, 37, 38, 39, 40, 46];
var sKey = String.fromCharCode(iKeyCode);
if (sKey !== "" && $.inArray(iKeyCode, aSpecialKeysForFirefox ) < 0 && !sKey.match(/[0-9]/)) {
ev.preventDefault();
}
});
Explanation
All Browsers handle jquerys keypress event differently. To make it work in FF the $.inArray check is added. As firefoxs keypress-event doesn't trigger when combinations like strg+tab are used, but the others do, the key.match approach still adds a little value to the latter, as it enables those combinations.

Maybe you are using bootstrap. If so, this may suffice:
<input type="text" data-mask="9999999">
Input mask

The following code is something I use extensively. I found the script in a forum, but modified and expanded it to accommodate my needs:
<script type="text/javascript">
// Restrict user input in a text field
// create as many regular expressions here as you need:
var digitsOnly = /[1234567890]/g;
var integerOnly = /[0-9\.]/g;
var alphaOnly = /[A-Za-z]/g;
var usernameOnly = /[0-9A-Za-z\._-]/g;
function restrictInput(myfield, e, restrictionType, checkdot){
if (!e) var e = window.event
if (e.keyCode) code = e.keyCode;
else if (e.which) code = e.which;
var character = String.fromCharCode(code);
// if user pressed esc... remove focus from field...
if (code==27) { this.blur(); return false; }
// ignore if the user presses other keys
// strange because code: 39 is the down key AND ' key...
// and DEL also equals .
if (!e.ctrlKey && code!=9 && code!=8 && code!=36 && code!=37 && code!=38 && (code!=39 || (code==39 && character=="'")) && code!=40) {
if (character.match(restrictionType)) {
if(checkdot == "checkdot"){
return !isNaN(myfield.value.toString() + character);
} else {
return true;
}
} else {
return false;
}
}
}
</script>
Different usage methods would be:
<!-- To accept only alphabets -->
<input type="text" onkeypress="return restrictInput(this, event, alphaOnly);">
<!-- To accept only numbers without dot -->
<input type="text" onkeypress="return restrictInput(this, event, digitsOnly);">
<!-- To accept only numbers and dot -->
<input type="text" onkeypress="return restrictInput(this, event, integerOnly);">
<!-- To accept only numbers and only one dot -->
<input type="text" onkeypress="return restrictInput(this, event, integerOnly, 'checkdot');">
<!-- To accept only characters for a username field -->
<input type="text" onkeypress="return restrictInput(this, event, usernameOnly);">

Add <script type="text/javascript" src="jquery.numeric.js"></script> then use
$("element").numeric({ decimal: false, negative: false });

shorter way and easy to understand:
$('#someID').keypress(function(e) {
var k = e.which;
if (k <= 48 || k >= 58) {e.preventDefault()};
});

This is a variation on Robert's answer that allows a single decimal point to be entered. If a decimal point has already been entered, only numbers are accepted as input.
JSFiddle - decimal number input
// Allow only decimal number input
$('#decimalInput').keypress(function (e) {
var a = [];
var k = e.which;
for (i = 48; i < 58; i++)
a.push(i);
// allow a max of 1 decimal point to be entered
if (this.value.indexOf(".") === -1) {
a.push(46);
}
if (!(a.indexOf(k) >= 0)) e.preventDefault();
$('span').text('KeyCode: ' + k);
});

I know that there are already many answers but for the sake of simplicity i would like to add another answer which is simple and self explanatory in which we do not have to remember keycodes and it also works across all browsers.
document.getElementById('myinput').onkeydown = function(e)
{
console.log(e.key);
//console.log(e.target.value);
switch (e.key)
{
case "1":
case "2":
case "3":
case "4":
case "5":
case "6":
case "7":
case "8":
case "9":
case "0":
case "Backspace":
return true;
break;
case ".":
if (e.target.value.indexOf(".") == -1)
{
return true;
}
else
{
return false;
}
break;
default:
return false;
}
}
<input type="text" placeholder="Enter Value" id="myinput" />

It's worth pointing out that no matter how tightly you manage to control this via the front end (Javascript, HTML, etc), you still need to validate it at the server, because there's nothing to stop a user from turning off javascript, or even deliberately posting junk to your form to try to hack you.
My advice: Use the HTML5 markup so that browsers which support it will use it. Also use the JQuery option previously suggested (the inital solution may have flaws, but it seems like the comments have been working through that). And then do server-side validation as well.

this will enable the numpad inputs also.
.keydown(function(event){
if(event.keyCode == 8 || event.keyCode == 46)
return true;
if(event.keyCode >= 96 && event.keyCode <= 105)
return true;
if(isNaN(parseInt(String.fromCharCode(event.keyCode),10)))
return false;
});

In order to block anything but numbers from being input into a text field but still allowing for other buttons to work (such as delete, shift, tab, etc.) look at a reference of the Javascript key codes; anything from 65 on up (to 222) can be blocked.
Using Jquery and Javascript, that would look like:
$('#textFieldId').keydown(function(event) {
if ( event.keyCode > 64 ) {
event.preventDefault();
}
});
The key codes will be the same in Javascript whether or not Jquery is used.

Here is my solution: a combination of the working ones below.
var checkInput = function(e) {
if (!e) {
e = window.event;
}
var code = e.keyCode || e.which;
if (!e.ctrlKey) {
//46, 8, 9, 27, 13 = backspace, delete, tab, escape, and enter
if (code == 8 || code == 13 || code == 9 || code == 27 || code == 46)
return true;
//35..39 - home, end, left, right
if (code >= 35 && code <= 39)
return true;
//numpad numbers
if (code >= 96 && code <= 105)
return true;
//keyboard numbers
if (isNaN(parseInt(String.fromCharCode(code), 10))) {
e.preventDefault();
return false;
}
}
return true;
};

I came across your question while trying to figure this out myself. Here is the solution that I came up with.
// Prevent user from entering non-numeric characters in number boxes.
(function (inputs) {
var input;
var f = function (e) {
var unicodeRe = /U\+(\d+)/;
// Chrome doesn't support the standard key property, so use keyIdentifier instead.
// Instead of the actual character that "key" returns, keyIdentifier returns
// A string such as "U+004F" representing the unicode character.
// For special characters (e.g., "Shift", a string containing the name of the key is returned.)
var ch = e.key || e.keyIdentifier;
var match = ch.match(unicodeRe);
// keyIdentifier returns a unicode. Convert to string.
if (match) {
ch = String.fromCharCode(Number.parseInt(match[1], 16));
}
console.log(ch);
if (ch.length === 1 && /[^0-9]/.test(ch)) {
if (!/[\b]/.test(ch)) { // Don't prevent backspace.
e.preventDefault();
}
}
};
for (var i = 0, l = inputs.length; i < l; i += 1) {
input = inputs[i];
input.onkeydown = f;
}
}(document.querySelectorAll("input[type=number],#routeFilterBox")));
Edit: I've discovered that my solution does not allow the user to enter numbers via the numpad in Chrome. The 0-9 keypad keys seem to be returning the character "`" for 0 and A-I for the rest of the number keys.

All of the answers are outdated, lengthy and will cause annoyance to your users. Most of them don’t even filter or allow pasted content.
Instead of filtering the input, do some validation before submitting the form and then also server-side.
HTML has validation included:
<input type="number" pattern="[0-9]+">
This also enables the number keyboard on mobile.

This is my plugin for that case:
(function( $ ) {
$.fn.numbers = function(options) {
$(this).keypress(function(evt){
var setting = $.extend( {
'digits' : 8
}, options);
if($(this).val().length > (setting.digits - 1) && evt.which != 8){
evt.preventDefault();
}
else{
if(evt.which < 48 || evt.which > 57){
if(evt.keyCode != 8){
evt.preventDefault();
}
}
}
});
};
})( jQuery );
Use:
$('#limin').numbers({digits:3});
$('#limax').numbers();

There is my current solution of numeric input, need to test in different browsers but seems to work
Support comma and period delimiter (czech native is comma), space and numpad/keyboard numbers input. Allow Ctrl+C Ctrl+A or Ctrl+X, arrow navigation and delete block Ctrl+V. React on escape key by blurring input.
Watch my Coffee script:
(($) ->
$.fn.onlyNumbers = ->
#each ->
$(#).keydown (e) ->
# get code of key
code = if e.keyCode then e.keyCode else e.which
return $(#).blur() if code is 27 # blur on escape
return if code in [46, 8, 9, 13] # 46, 8, 9, 27, 13 = backspace, delete, tab, escape, and enter
return if (e.ctrlKey or e.metaKey) and code in [65, 67, 88] # ctrl|command + [a, c, x]
return if code in [96..105] # numpad numbers
return if code in [48..57] # numbers on keyboard
return if code in [35..39] # 35..39 - home, end, left, right
return if code in [188, 190, 32] # comma, period, space
return if code in [44] # comma, period,
e.returnValue = false # IE hate you
e.preventDefault();
$(#).keypress (e) ->
code = if e.keyCode then e.keyCode else e.which
return if code in [44, 46, 32] # comma, period, space
return if code in [48..57] # numbers on keyboard
e.returnValue = false # IE hate you
e.preventDefault();
) jQuery
You can get compiled Javascript here http://goo.gl/SbyhXN

My functions:
$('.input_integer_only').on('input', function(e) {
$(this).val($(this).val().replace(/[^0-9]/g, ''));
});
$('.input_float_only').on('input', function(e) {
var $var = $(this).val().replace(/[^0-9\.]/g, '');
var $aVar = $var.split('.');
if($aVar.length > 2) {
$var = $aVar[0] + '.' + $aVar[1];
}
$(this).val($var);
});

You can make changes to accept the keycode for Ctrl keys: 17, 18, 19, 20.
Then your code will be like:
function numbersonly(e, decimal) {
var key;
var keychar;
if (window.event)
key = window.event.keyCode;
else if (e)
key = e.which;
else
return true;
keychar = String.fromCharCode(key);
if ((key==null) || (key==0) || (key==8) || (key==9) || (key==13) || (key==27) || (key==17) || (key==18) || (key==19) || (key==20))
return true;
else if ((("0123456789").indexOf(keychar) > -1))
return true;
else if (decimal && (keychar == "."))
return true;
else
return false;
}

document.getElementById('myinput').onkeydown = function(e) {
if(!((e.keyCode > 95 && e.keyCode < 106)
|| (e.keyCode > 47 && e.keyCode < 58)
|| e.keyCode == 8
|| e.keyCode == 9)) {
return false;
}
}

You can do like this to accept only Numbers in text Box,
function onChange(event){
var ckeckChars = /[^0-9]/gi;
if(checkChars.test(event.target.value)) {
event.target.value = event.target.value.replace(ckeckChars,"");
}

I am using below in Angular to restrict character
in HTML
For Number Only
<input
type="text"
id="score"
(keypress) ="onInputChange($event,'[0-9]')"
maxlength="3"
class="form-control">
for Alphabets Only
<input
type="text"
id="state"
(keypress) ="onInputChange($event,'[a-zA-Z]')"
maxlength="3"
class="form-control">
In TypeScript
onInputChange(event: any, inpPattern:string): void {
var input = event.key;
if(input.match(inpPattern)==null){
event.preventDefault();
}
}

This JavaScript function will be used to restrict alphabets and
special characters in Textbox , only numbers, delete, arrow keys and
backspace will be allowed. JavaScript Code Snippet - Allow Numbers
in TextBox, Restrict Alphabets and Special Characters
Tested in IE & Chrome.
JavaScript function
<script type="text/javascript">
/*code: 48-57 Numbers
8 - Backspace,
35 - home key, 36 - End key
37-40: Arrow keys, 46 - Delete key*/
function restrictAlphabets(e){
var flag = false;
var x = e.which || e.keycode;
if ((x >= 48 && x <= 57) || x == 8 ||
(x >= 35 && x <= 40) || x == 46)
flag = true;
else
flag = false;
if (flag && e.keyCode === 46 && $(e.currentTarget).val().split('.').length === 2) {
flag = false;
}
return flag;
}
</script>
HTML Source Code with JavaScript
<html>
<head>
<title>JavaScript - Allow only numbers in TextBox (Restrict Alphabets and Special Characters).</title>
<script type="text/javascript">
/*code: 48-57 Numbers
8 - Backspace,
35 - home key, 36 - End key
37-40: Arrow keys, 46 - Delete key*/
function restrictAlphabets(e){
var x=e.which||e.keycode;
if((x>=48 && x<=57) || x==8 ||
(x>=35 && x<=40)|| x==46)
return true;
else
return false;
}
</script>
</head>
<body style="text-align: center;">
<h1>JavaScript - Allow only numbers in TextBox (Restrict Alphabets and Special Characters).</h1>
<big>Enter numbers only: </big>
<input type="text" onkeypress='return restrictAlphabets(event)'/>
</body>
</html>
Refrence

You can handle te event on html by introducing keypresshandler function
function keypresshandler(event)
{
var charCode = event.keyCode;
//You condition
if (charCode == 58 ){
event.preventDefault();
return false;
}
}

Javascript is often used on the browser client side to perform simple tasks that would otherwise require a full postback to the server. Many of those simple tasks involve processing text or characters entered into a form element on a web page, and it is often necessary to know the javascript keycode associated with a character. Here is a reference.
Press a key in the text box below to see the corresponding Javascript key code.
function restrictCharacters(evt) {
evt = (evt) ? evt : window.event;
var charCode = (evt.which) ? evt.which : evt.keyCode;
if (((charCode >= '48') && (charCode <= '57')) || (charCode == '44')) {
return true;
}
else {
return false;
}
}
Enter Text:
<input type="text" id="number" onkeypress="return restrictCharacters(event);" />