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How to allow only numbers in a textarea using jQuery?

I've seen a similar question on SO but my approach is slightly different. I have a textarea that I want to accept only numbers as an input. Currently all inputs are allowed and the error alert isn't triggered.
I think the problem may be that the key being pressed isn't being passed into my validate function, but I'm not sure how to do that without using the html onkeypress which I'm trying to avoid using.
HTML:
<textarea id="noteNumberInput" placeholder="Note number"></textarea>
JS:
$(document).ready(function () {
var noteNumberInput = document.getElementById("noteNumberInput");
//VALIDATE NOTE NUMBER TEXTAREA
function validate() {
var keycode = (key.which) ? key.which : key.keyCode;
//comparing pressed keycodes
if (keycode < 48 || keycode > 57) {
alert("Please only enter the note number e.g. '1', '2' etc.")
return false;
}
}
noteNumberInput.addEventListener("keypress", validate);
});

Your function needs the key parameter:
function validate(key) {
....

jquery restrict only < and > symbol in textbox

Code:
$j("#<%= txtGradingScale.ClientID%>").bind("keypress", function (e)
{
var keyed = $j(this).val();
$j("#<%= txtGradingScale.ClientID%>").html
(keyed.replace(/\<>/gi, ''));
});
Have to restrict greter than and lesser than symbol in textbox while entering .
above code is not working pls suggest the method .i tried keyCode and Charcode but it's not working

The reason it's not working is because the regular expression /\<>/ (the escape character \ is not needed) is looking for <> and not the characters by themselves, what you want to do is:
$('textarea[name="test"]').keyup(function(e) {
$(this).val($(this).val().replace(/[<>]/ig, ''));
});
This will match any instance of the < and > characters no matter what order they appear in.
You should also use keyup instead of keypress because keypress will only trigger after the next key gets hit, while keyup will trigger whenever the key is released.
Fiddle

You want to test using e.which and compare with corresponding codes for < and >. If you return false or invoke e.preventDefault() when they are encountered, that should do it.
$('#myText').on('keypress', function(e) {
if( e.which === 60 || e.which === 62 ) {
e.preventDefault();
}
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<input type="text" name="myText" id="myText"/>

Allow only numbers in Input field IOS

Ok Well. I want to restrict input field to accept only numbers with maxlength 5 characters.
My Try:
HTML
<input type="number" maxlength="5" onKeyDown="numbersOnly(event);/>
<input type="text" pattern= "[0-9]" onKeyDown="numbersOnly(event);/>
Javascript
function numbersOnly(event,length)
{
return event.ctrlKey || event.altKey
|| (95<event.keyCode && event.keyCode<106)
|| (event.keyCode==8) || (event.keyCode==9)
|| (event.keyCode>34 && event.keyCode<40)
|| (event.keyCode==46)
|| (event.keyCode>47)&&(event.keyCode<=57) ;
}
All works in firefox. But when i check with safari ipad, it accepts special characters like ()#!#$&. I used alert function for debugging. It returns same keyCode for # and 2 , 3 and # and so on. I tried keyUp,keyPress events and event.charCode,event.which,event.key. Nothing works
So how to differentiate it and i need support for backspace , enter , delete, arrow keys also.

I've made this once and haven't been able to break it. Tested on iPad.
// Prevent NULL input and replace text.
$(document).on('change', 'input[type="number"]', function (event) {
this.value = this.value.replace(/[^0-9]+/g, '');
if (this.value < 1) this.value = 0;
});
// Block non-numeric chars.
$(document).on('keypress', 'input[type="number"]', function (event) {
return (((event.which > 47) && (event.which < 58)) || (event.which == 13));
});
This also accounts for copy/paste and drag and drop text, which people often forget. You can add the max-length to the onchange.

Using type="number" on an input prevents you from reading non-numerical input values via input.value (it will then return an empty string) and thus eliminates the possibility of filtering invalid user input (+-.e) while keeping the valid numbers. Thus you have to use type="text". Example:
$('.input-number').on('input', function (event) {
this.value = this.value.replace(/[^0-9]/g, '');
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input class="input-number" type="text" maxlength="5">
If you want the text-cursor not to move when pasting or typing invalid input, have a look at my answer to a similar question here: HTML input that takes only numbers and the + symbol

Be careful the iOS keyCodes are not the same desktop computers. See IOS keyCodes in Javascript
<input type="number" maxlength="5" onkeypress="numbersOnly(event);/>
var numbersOnly = function(event) {
if(event.keyCode >= 48 && event.keyCode <= 57) {
return false;
} else {
event.preventDefault();
}
}

If you want to enter the only numbers in input type number fields. this will be helpful, It will work on iPhone and iPad as well.
$(document).on('keypress', 'input[type="number"]', function (event) {
return event.code.includes('Digit') || event.code.includes('Numpad') || event.code.includes('Period');;
});

How to use Javascript to filter and ignore keypresses on an input field?

I need to stop accepting input (keystrokes) on an HTML form input field when the length limit has been reached. In straight-up HTML I can do this with maxlength="3" or whatever the length is, but I would like to handle it through Javascript if possible so I can do it together with the next requirement.
I also need to filter the input so that if a field is numeric only numbers can be typed, and if there's a mask or regex any inputs conform to the mask/regex.
Is there a "standard" way to do this in, Javascript, particularly in Dojo 1.9? (I know everybody uses JQuery but we use Dojo because.)

For dojo, if you need any sort of validation, I would use the ValidationTextBox, which takes "maxLength" as a property AND allows for all sorts of nifty validation schemes. The reference for ValidationTextBox is here:
http://dojotoolkit.org/reference-guide/1.9/dijit/form/ValidationTextBox.html

I used pure Javascript because I am not familiar with Dojo, but these event listeners can probably be cleaned up with Dojo.
var input = document.getElementsByTagName('input')[0],
error = document.getElementById('error');
input.addEventListener('keypress', function(e) {
if(e.which < 48 || e.which > 57) {
e.preventDefault();
error.innerHTML = 'Must be a digit';
} else if(e.target.value.length >= 3) {
e.preventDefault();
error.innerHTML = 'Cannot be more than 3 digits';
} else {
error.innerHTML = '';
}
});
We listen to a keypress and then, to make sure it is a digit, we seek that the key pressed was between 48-57 (0-9). If not, then we prevent the key press and show an error. Then we check the input's current length. If it is too long, then prevent the key press and show an error. Otherwise, it worked and we allow the event and clear the error.

You maybe looking for this:
<input id="text" type="text"/>
$('#text').on('keypress',function(e){
var numero = this.value.length;
console.log(this.value.length);
if (e.which != 8 && e.which < 48 || e.which > 57)
{
return false
}
else if (numero === 3 && e.which != 8){
return false //alert user here
}else{
return true // allow backspace only (8)
}
}
);
DEMO

Restrict characters in input field

Is there a way to block users from writing specific characters in input fields? I tried the code below, but when a user enters disallowed characters, they appear for a brief period before disappearing. I want the input to remain unchanged when invalid characters are written.
I want to use onchange because other restriction methods do not seem to work on mobile devices. The problem I want to solve is that characters appear briefly before being removed.
function checkInput(ob) {
const invalidChars = /[^0-9]/gi;
if(invalidChars.test(ob.value)) {
ob.value = ob.value.replace(invalidChars, "");
}
};
<input class="input" maxlength="1" onChange="checkInput(this)" onKeyup="checkInput(this)" type="text" autocomplete="off" />

you can use try this,
$('.input').keyup(function () {
if (!this.value.match(/[0-9]/)) {
this.value = this.value.replace(/[^0-9]/g, '');
}
});
SEE THIS FIDDLE DEMO
Updated :
You can try this Code,
$(document).ready(function() {
$(".input").keydown(function (e) {
// Allow: backspace, delete, tab, escape and enter
if ($.inArray(e.keyCode, [46, 8, 9, 27, 13, 110]) !== -1 ||
// Allow: Ctrl+A
(e.keyCode == 65 && e.ctrlKey === true) ||
// Allow: home, end, left, right
(e.keyCode >= 35 && e.keyCode <= 39)) {
// let it happen, don't do anything
return;
}
// Ensure that it is a number and stop the keypress
if ((e.shiftKey || (e.keyCode < 48 || e.keyCode > 57)) && (e.keyCode < 96 || e.keyCode > 105)) {
e.preventDefault();
}
});
});
SOURCE
SEE UPDATED FIDDLE DEMO
UPDATED FOR ANDROID:
<EditText
android:id="#+id/editText1"
android:inputType="number"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="#+id/textView1"
android:layout_marginTop="58dp"
android:layout_toRightOf="#+id/textView1"
android:maxLength="1" >
</EditText>
I think it may help you... using android:inputType="number" you can do that.

A combination of keypress and paste events does a trick:
var text = document.getElementById('text');
text.onkeypress = text.onpaste = checkInput;
function checkInput(e) {
var e = e || event;
var char = e.type == 'keypress'
? String.fromCharCode(e.keyCode || e.which)
: (e.clipboardData || window.clipboardData).getData('Text');
if (/[^\d]/gi.test(char)) {
return false;
}
}
<input class="input" maxlength="10" id="text" type="text" autocomplete="off" />
This code prevents from typing or pasting anything but a number. Also no blinking and invalid characters don't show up.
Works in IE7+.
Demo: http://jsfiddle.net/VgtTc/3/

All answers given so far suffer from at least one of the following accessibility issues:
They validate key codes, which does not work with non-QWERTY keyboard layouts.
They do not cover all input methods; especially drag&drop is often forgotten.
They alter the value, which resets the position of the caret.
They use the pattern attribute, but this does not provide feedback until the form is submitted.
Wouldn't it be a much better idea to actually validate the input before it's inserted?
The beforeinput event fires before the input's value is changed. The event has a data property which describes the content that the user wants to add to the input field. In the event handler, you simply check the data attribute, and stop the event chain if it contains disallowed characters.
We end up with the following very simple, very short code.
const input = document.getElementById("input");
const regex = new RegExp("^[0-9]*$");
input.addEventListener("beforeinput", (event) => {
if (event.data != null && !regex.test(event.data))
event.preventDefault();
});
<label for="input">Enter some digits:</label>
<input id="input" />
Some closing notes:
Accessibility: Provide a clear explanation of what input format is expected from the user. For example, you can use the title attribute of the input to show a tooltip explaining the expected format.
Security: This is client-side validation, and does not guarantee that the pattern is enforced when the form is sent to a server. For that, you'll need server-side validation.

Here's a little hack you could try: DEMO
What it does is that it colors every input text white and then changes it back to black if it suits your requirements. If you could live with the bit of lag that occurs when you enter a valid character.
function checkInput(ob) {
var invalidChars = /[^0-9]/gi
if (invalidChars.test(ob.value)) {
ob.value = ob.value.replace(invalidChars, "");
}
else {
document.getElementById('yourinput').style.color = '#000';
}
};
function hideInput(ob) {
document.getElementById('yourinput').style.color = '#FFF';
};
html
<input id="yourinput" class="input" maxlength="1" onKeydown="hideInput(this)" onKeyup="checkInput(this)" type="text" autocomplete="off" />
css
input {color:#FFF;}

check this code,
$('.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();
});
​

<input id="testInput"></input>
<script>
testInput.onchange = testInput.oninput = restrict;
function restrict() {
testInput.value = testInput.value.replace(/[^a-z]/g, "");
}
</script>
I came up with something slightly different. oninput instead of onkeyup/onkeydown, and onchange instead of onpaste.

I restrict invalid characters on both keypress and paste events like:
<input type="text" onkeydown="validateKey(event)" onpaste="validatePaste(this, event)">
And define functions to handle these events inside tab or a separate javascript file:
<script>
function validateKey(e) {
switch(e.keyCode) {
case 8,9,13,37,39:
break;
default:
var regex = /[a-z .'-]/gi;
var key = e.key;
if(!regex.test(key)) {
e.preventDefault();
return false;
}
break;
}
}
function validatePaste(el, e) {
var regex = /^[a-z .'-]+$/gi;
var key = e.clipboardData.getData('text')
if (!regex.test(key)) {
e.preventDefault();
return false;
}
}
</script>