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How can I prevent other characters from being inputted on an input except numbers using Javascript

I am using Vue.JS (Bootstrap-Vue) to build a form, my input has the following code:
<b-form-input
v-mask="'####'"
number
type="number"
no-wheel
pattern="[0-9]"
step="1"
:class="{ 'hasError': $v.form.dobYear.$error }"
v-model.number="$v.form.dobYear.$model"
class="form-input"
name="year"
id="year"
maxlength="4"
min="1900"
max="2020"
#keydown="filterKey"
></b-form-input>
When a user presses down I want to prevent more than 4 characters to be entered, this works, but when testing, I can see period and dashes and other similar characters can also be added into the input and ignores the maximum of 4 characters. How can I update the following code to ensure nothing but numbers can be added to my input on mobile. I'm trying to detect if any of those unwanted keys are pressed then prevent the default action. (I've tested on Android Chrome)
filterKey(e) {
const value = e.target.value;
const key = e.key;
console.log(value, this.amount);
if (String(value).length === 4) {
//check if a number is pressed after 4 have been entered
if (!isNaN(Number(key))) {
e.preventDefault();
return;
} else if (key == 190 || key == 189 || key == 107 || key == 69) {
e.preventDefault();
return;
}
}
}

The following snippet will not allow anything to be entered into the input element if the length of the input's value is already 4, or if a non-numeric character is typed (but will allow 'Backspace' and 'Delete' keys):
EDIT : Implemented Hiws' suggestion to let the user type in numbers even if the length is 4, if some text is selected in the input element
function filterKey(e) {
let previousValue = e.target.value;
let key = e.keyCode || e.charCode;
if (key != 8 && key != 46) { // Ignore backspace and delete
if (
// preventDefault if length of input is 4 and no text is selected in the input
( String(e.target.value).length >= 4 && e.target.selectionStart === e.target.selectionEnd ) ||
// preventDefault if entered a space or non-number
!e.key.trim() || isNaN(e.key)
) {
// Prevent input if input length crosses 4,
// or if input is not a number
e.preventDefault();
// Include below line only if you have no other event listeners on the element, or its parents
e.stopImmediatePropagation();
return;
}
}
}

You block keys other than numbers only if number value already equals to 4. Try changing your blocking logic to:
if (String(value).length > 4 || !isNaN(Number(key)) || unwanted keyCodes) {
e.preventDefault();
return;

You can use a regex to test against the value of the input field and avoid messing with keyCodes.
if ( !/^[0-9]{0,4}$/.test(String(value)) ) {
e.preventDefault();
return;
}

Maxlength in Webview textfields for PhoneGap apps on Android

I am trying to implement maxlength in PhoneGap for Android but am not able to restrict characters cause it never fetches proper character code. Character code for delete key from below code is same as character code for any other key.
$(".limit-thirtyfive").bind("paste", function(e) {
// access the clipboard using the api
if (e.keyCode != 8 || e.keyCode != 46) {
if ($(this).val().length >= 33) {
$(this).val($(this).val().substr(0, 33));
}
}
});
$('.limit-ten').keyup(function(e) {
if (e.keyCode != 8 || e.keyCode != 46) {
if ($(this).val().length >= 10) {
$(this).val($(this).val().substr(0, 10));
}
}
});

Length Restriction on General
You can simply use maxlength attribute of the input element you are referring to.
<input type="text" maxlength="5"/>
Restricting Special Characters
For getting this done, you may want to use onchange event of input fields. The example below restricts user to enter character 'a'.
$('your_input').onchange(function(){
$(this).val($(this).val().replace(/a/g, ''));
});

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>

Which is the proper way of filtering numeric values for a text field?

I'm working on a textfield working with the kind of validation that wouldn't let you enter other than numeric values. As so, my initial code looked quite simple and similar to this:
$(textField).onKeyPress(function(e) {
if (e.which < 48 && e.which > 57)
e.preventDefault();
});
This is fairly strightforward, but turns that (in the latest version of all browsers) Firefox will make this also prevent movement with the arrow keys and delete/backspace keys, whereas the other browsers would not.
Looking around I found that I would need to also check for these keys, and check for different properties exposed in the e event reference.
My final code looks something like this:
$(textField).onKeyPress(function(e) {
var code = e.which || e.keyCode;
if (code > 31 // is not a control key
&& (code < 37 || code > 40) // is not an arrow key
&& (code < 48 || code > 57) // is not numeric
&& (code != 46) // is not the delete key
)
e.preventDefault();
});
However, this feels to be too much to solve a fairly simple problem as just preventing non-numeric.
What am I doing wrong? Which is the best practice in terms of this kind of validation?

We'll respond to both keypresses, and the blur event. When somebody press a key, we check to see if the key entered is a number. If it is, we permit it. Otherwise, we prevent it.
If the field is blurred, we remove any non-numerical values, and all those values that follow. This will prevent the user from pasting in non-numerical strings:
$("#textfield").on("keypress blur", function(e){
if ( e.type === "keypress" )
return !!String.fromCharCode(e.which).match(/^\d$/);
this.value = this.value.replace(/[^\d].+/, "");
});
Demo: http://jsfiddle.net/jonathansampson/S7VhV/5/

Working demo http://jsfiddle.net/Pb2eR/23/ Updated Copy/Paste demo: http://jsfiddle.net/Pb2eR/47/ (In this demo wit you copy paste string with characters it won't allow else it will allow number to be copy pasted: tested in safari)
Demo for arrow key to work http://jsfiddle.net/gpAUf/
This will help you.
Note: in this version even if you copy paste it will set it to empty input box, tested in safari lion osx :)
Good Link: [1] How to allow only numeric (0-9) in HTML inputbox using jQuery?
code
$(".hulk").keyup(function(){
this.value = this.value.replace(/[^0-9\.]/g,'');
});
​
html
<input type="text" class="hulk" value="" />
​
Update for copy paste stuff
$(".hulk").keyup(function(){
this.value = this.value.replace(/[^0-9\.]/g,'');
});
$(".hulk").bind('input propertychange', function() {
this.value = this.value.replace(/[^0-9\.]/g,'');
});​
code from another demo
$(".hulk").bind('input propertychange', function(event) {
if( !(event.keyCode == 8 // backspace
|| event.keyCode == 46 // delete
|| (event.keyCode >= 35 && event.keyCode <= 40) // arrow keys/home/end
|| (event.keyCode >= 48 && event.keyCode <= 57) // numbers on keyboard
|| (event.keyCode >= 96 && event.keyCode <= 105)) // number on keypad
) {
event.preventDefault(); // Prevent character input
}
this.value = this.value.replace(/[^0-9\.]/g,'');
});
​

this will allow both int.
it also removes text if user copy and paste with mouse.
$(document).ready(function () {
$('#textfield').bind('keyup blur', function (e) {
if (e.type == 'keyup') {
if (parseInt($(this).val()) != $(this).val()) {
$(this).val($(this).val().slice(0, $(this).val().length - 1));
}
} else if (e.type == 'blur') {
$(this).val('');
}
});
});