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How to remove characters when input not matches regex in JS

<input id="myInput" onblur="myFunction()">
<script>
function myFunction() {
var value= document.getElementById('myInput').value;
var regexCharacter = /[0-9|,]+/g;
strFirst = value.replace(regexCharacter, '')
document.getElementById('myInput').value = strFirst
}
</script>
I want to replace '' when the input does not match the regex's.
My regex just allow input number and comma.
My function is replace when input matching, i want to replace when it's not matching.
E.g a12,b2a => 12,2
can anyone help me, thanks.

Use /[^0-9|,]+/g as your regex. The ^ mark is used to match any character that's not in range.
Pro tip: You dont have to memorize all these tokens, just use a tool like https://regex101.com/

First of all, your function is not called to check the value with reqex.
then yout reqex replace "" when is number not charactors
<input type="text" id="myInput">
<script>
myInput.addEventListener("input", function (e) {
var value= document.getElementById('myInput').value;
strFirst = value.replace(/[^0-9.]/g, '').replace(/(\..*?)\..*/g, '$1')
document.getElementById('myInput').value = strFirst
});
</script>
in this code you can write number whith dot
whith this reqex
value.replace(/[^0-9.]/g, '').replace(/(..?)../g

I think you should edit your regex to match letters instead of numbers. Like this: /[a-zA-Z|]+/g

Get input[text] value before special characters are trimmed in typescript

I have a from. User can fill an input field with text that contains special characters like \n, \t and etc. I have to replace these special characters and add it back as value of the input field.
for example:
user input is: hello, \n how are you doing? \t this is a sample text.
This is what I need: hello, newline how are you doing? tab this is a sample text.
I am using JQuery and Typescript 2.4

How about this?
$('#input').keyup(function () {
var val = $(this).val();
var replaceWithBr = val.replace(/\\n/g, '<br>');
var replaceWithTab = replaceWithBr.replace(/\\t/g, ' ');
$('#result').html(replaceWithTab);
})
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="text" id="input">
<div id="result"></div>

Javascript strip after X characters prior to form submit

UPDATE** Using the solutions provided below I added this with no luck?
<script>
$('.LogIn_submit').on('click',function(){
var value=$('#Log_In_group_2_FieldB').val();
value=value.replace(/^\s\d{6}(?=\-)&/, '')
alert(value);
});
</script>
Here are the form elements if, hoping it's a simple fix:
<input id="Log_In_group_2_FieldB" name="Log_In_group_2_FieldB" type="password" value="<?php echo((isset($_GET["invalid"])?ValidatedField("login","Log_In_group_2_FieldB"):"".((isset($_GET["failedLogin"]) || isset($_GET["invalid"]))?"":((isset($_COOKIE["RememberMePWD"]))?$_COOKIE["RememberMePWD"]:"")) ."")); ?>" class="formTextfield_Medium" tabindex="2" title="Please enter a value.">
<input class="formButton" name="LogIn_submit" type="submit" id="LogIn_submit" value="Log In" tabindex="5">
/***** Beginning Question ******/
Using this question/answers's fiddle I can see how they used javascript like this:
$('.btnfetchcont').on('click',function(){
var value=$('#txtCont').val();
value=value.replace(/^(0|\+\d\d) */, '')
alert(value);
});
I currently have a value that starts with 6 characters, ends in a dash and the up to 3 digits can follow the dash.
Exmaple 1: 123456-01
Example 2: 123456-9
Example 3: 123456-999
I've tried to insert a - in the value.replace cod with no luck. How do I remove the - and any values after this on submit so that I'm only submitting the first 6 digits?

Seems that you want to have only first 6 characters from the string.
Use .split() or substring(start, end) to get the parts of string.
var string = "123456-01";
console.log(string.split('-')[0]);
console.log(string.substring(0,6));
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

You can use split instead of regex
value=value.split("-")[0];
fix for your regex
/(-[0|\+\d\d]*)/g
function extractNumber(value){
return value.replace(/(-[0|\+\d\d]*)/g, '');
}
console.log(extractNumber("123456-01"));
console.log(extractNumber("123456-9"));
console.log(extractNumber("123456-999"));

Edit: the .split('-') answer is better than the following, imo.
Assuming you always want just the first 6 characters, something like this should do what you want:
$('.btnfetchcont').on('click',function(){
var value = $('#txtCont').val();
value = value.substr(0, 6);
alert(value);
});
or combine the two lines:
var value = $('#txtCont').val().substr(0, 6);
Read about .substr() here.
If you want to get everything before the dash, do something like this:
var value = $('#txtCont').val().match(/(\d*)-(\d*)/);
value is now an array where value[0] is the original string, value[1] is every digit before the dash, and value[2] is every digit after the dash.
This works for digits only. If you want any character instead of just digits, replace \d with .. i.e: .match(/(.*)-(.*)/).

Textbox should allow only Hexa decimal values

I have a textbox and i can enter only 2 digits. What i want is that user can only input Hexa values in it like 12,a0,0a (2 digits) if user enters any ather value , it will not be entered. Can you please help.
<input onkeyup=validateHexa(this); class='nbb' maxlength='2' value='??'/>
function validateHexa(ele){
var control = ele.value;
var regExp = new RegExp(/^([A-Fa-f0-9]{2}){8,9}$/);
if (!regExp.test(control))
ele.value="true";
}

You can do something like this:
function replaceInput(ele) {
var re = /[^A-Fa-f0-9]/g;
ele.value = ele.value.replace(re, '');
}
<input onkeyup=replaceInput(this); class='nbb' maxlength='2' placeholder='??' pattern="[A-Fa-f0-9]{2}"/>
JSFiddle

hello there you should try Regular expression like ([aA-hH 0-9]{2})
please comment if any issue :)

Regular expression on textarea

I'm having a bit of trouble validating a form I have, I can check for only letters, numbers and a full stop ("period") in a single text input, but I can't for the life of me get it to work at all on a textarea field.
in my validation I have this:
var usernamecheck = /^[A-Za-z0-9.]{5,1000}$/;
the validation I've tried that doesn't work on the textarea ($ITSWUsers) is:
if(!document.all.ITSWUsers.value.match(usernamecheck))
{
alert ("Please write the usernames in the correct format (with a full stop between first and last name).");
return false;
}
however, the following on a 'input type="text"' works just fine on the same form
if(!document.all.SFUsersName1.value.match(usernamecheck))
{
alert("Usernames can only contain letters, numbers and full stops (no spaces).");
return false;
}
I need it to validate usernames, 1 name per line
e.g.
John.smith
Peter.jones1
these are both OK but the following wouldn't be:
John Smith
David.O'Leary
3rd.username
any help/pointers with this would be greatly appreciated
(I only know basic html/php/javascript)

To validate line by line, I'd use the split function to turn each line into an array. Then, loop through the array and run your RegEx on each line. That way, you can report exactly what line is invalid. Something like this:
<textarea id="ITSWUsers"></textarea>
<button onclick="Validate()">Validate</button>
<script>
var usernamecheck = /^[A-Za-z0-9]{5,1000}\.[A-Za-z0-9]{5,1000}$/;
function Validate()
{
var val = document.getElementById('ITSWUsers').value;
var lines = val.split('\n');
for(var i = 0; i < lines.length; i++)
{
if(!lines[i].match(usernamecheck))
{
alert ('Invalid input: ' + lines[i] + '. Please write the usernames in the correct format (with a full stop between first and last name).');
return false;
}
}
window.alert('Everything looks good!');
}
</script>

I'd trim the input from the textarea using JQuery (or a JS function), and then use this regex:
/^([A-Za-z0-9]+\.[A-Za-z0-9]+(\r)?(\n)?)+$/
Like so:
function testFunc()
{
var usernamecheck = /^([A-Za-z0-9]+\.[A-Za-z0-9]+(\r)?(\n)?)+$/;
if(!$.trim(document.all.ITSWUsers.value).match(usernamecheck))
{
alert ("Please write the usernames in the correct format (with a full stop between first and last name).");
return false;
}
}
<textarea id="ITSWUsers" cols="50" rows="10">
John.smith
Peter.jones1
</textarea>
<button onclick="testFunc()">Click Me</button>
See it working here:
http://jsfiddle.net/DkLPB/