Develop Reference

Pure Javascript - get beginning position of current line in a multiline textarea

I'm looking for a pure javascript answer as that reflects my projects scope. jQuery answers will not be marked correct, but are welcomed for future question seekers. Side note: I am also not interested in third party libraries.
I'm trying to get the first position (0) of the current line (current is based of selectionStart the chance the user selects more than 1 line) in a multiline textarea, but translate that to caret index.
What have I tried? Nothing pretty:
for ( i = 0; i < this.selectionStart; i++ ) {
if (this.value.substr(i,1).match(/\r?\n|\r/)) {
lineStartIndx = i + 1
}
}
This is proving to be costly when iterating textareas with huge amounts of lines. My personal usage of this will not be executed every keydown, however, I just used it as an example. Are there any better methods, built in or otherwise to emulate this outcome?
My full example:
var input = document.getElementById("ta");
var output = document.getElementById("output");
let pattern = /\r?\n|\r/;
var lineNum, lineStartIndx;
input.addEventListener("keydown", function(e) {
taHandler(this);
})
input.addEventListener("click", function(e) {
taHandler(this);
})
function taHandler(elem) {
lineNum = getLineNumForSelection(elem);
let caretPos = elem.selectionStart;
lineStartIndx = 0;
for ( i = 0; i < caretPos; i++ ) {
if (elem.value.substr(i,1).match(pattern)) {
lineStartIndx = i + 1
}
}
output.innerHTML = "Selection Start: " + caretPos + " Selection End: " + elem.selectionEnd +
" <br> Line Number: " + lineNum.start +
"<br>Line Start Position: " + lineStartIndx;
}
function getLineNumForSelection(sel) {
return {
'start' : sel.value.substr(0, sel.selectionStart).split(pattern).length,
'end' : sel.value.substr(0,sel.selectionEnd).split(pattern).length
};
}
<textarea id="ta" rows="5" cols="50">
Line one
Line two
Line three
Line four
</textarea>
<hr>
<div id="output"></div>

The method in my copy of the snippet splits the content into lines and uses the .length property instead of a loop so it looks "prettier" but according to time complexity of javascript's .length may not be any faster since there is nothing in the spec that prevents slow browser implementation.
Two side notes about the code, I'd use lineStartIndex, not lineStartIndx without the e. Since lineNum is an array, I'd use lineNumArray or selLineNums or something that is more obvious since variables ending in num are generally integers.
var input = document.getElementById("ta");
var output = document.getElementById("output");
let pattern = /\r?\n|\r/;
var lineNum, lineStartIndx;
input.addEventListener("keydown", function(e) {
taHandler(this);
})
input.addEventListener("click", function(e) {
taHandler(this);
})
function taHandler(elem) {
lineNum = getLineNumForSelection(elem);
let caretPos = elem.selectionStart;
lineStartIndx = 0;
// begin modified code
let lines = elem.value.split(pattern),
lineIndex = 0;
while ( (lineIndex + 1 ) < lineNum.start ) {
lineStartIndx += parseInt( lines[lineIndex].length ) + 1;
lineIndex++;
}
// end modified code
// begin replaced code
for ( i = 0; i < caretPos; i++ ) {
if (elem.value.substr(i,1).match(pattern)) {
lineStartIndx = i + 1
}
}
// end replaced code
output.innerHTML = "Selection Start: " + caretPos + " Selection End: " + elem.selectionEnd +
" <br> Line Number: " + lineNum.start +
"<br>Line Start Position: " + lineStartIndx;
}
function getLineNumForSelection(sel) {
return {
'start' : sel.value.substr(0, sel.selectionStart).split(pattern).length,
'end' : sel.value.substr(0,sel.selectionEnd).split(pattern).length
};
}
<textarea id="ta" rows="5" cols="50">
Line one
Line two
Line three
Line four
</textarea>
<hr>
<div id="output"></div>

Adding a space after 4 chars in an input [duplicate]

I'm really new in JavaScript and I would like to add to my input text, space insertion for IBAN account registering.
<input type="text" name="iban" onkeyup="if(this.value.length > 34){this.value=this.value.substr(0, 34);}" />
There is my input field; could someone tell me how I can do this?

The existing answers are relatively long, and they look like over-kill. Plus they don't work completely (for instance, one issue is that you can't edit previous characters).
For those interested, according to Wikipedia:
Permitted IBAN characters are the digits 0 to 9 and the 26 upper-case Latin alphabetic characters A to Z.
Here is a relatively short version that is similar to the existing answers:
document.getElementById('iban').addEventListener('input', function (e) {
e.target.value = e.target.value.replace(/[^\dA-Z]/g, '').replace(/(.{4})/g, '$1 ').trim();
});
<label for="iban">iban</label>
<input id="iban" type="text" name="iban" />
As stated above, the caveat is that you can't go back and edit previous characters. If you want to fix this, you would need to retrieve the caret's current position by initially accessing the selectionEnd property and then setting the caret's position after the regex formatting has been applied.
document.getElementById('iban').addEventListener('input', function (e) {
var target = e.target, position = target.selectionEnd, length = target.value.length;
target.value = target.value.replace(/[^\dA-Z]/g, '').replace(/(.{4})/g, '$1 ').trim();
target.selectionEnd = position += ((target.value.charAt(position - 1) === ' ' && target.value.charAt(length - 1) === ' ' && length !== target.value.length) ? 1 : 0);
});
<label for="iban">iban</label>
<input id="iban" type="text" name="iban" />
You will notice that there is a slight issue when the character after the caret is a space (because the space wasn't accounted for when initially retrieving the caret's position to begin with). To fix this, the position is manually incremented if the succeeding character is a space (assuming a space was actually added - which is determined by comparing the length before and after replacing the characters).

Using plain-JavaScript, I'd suggest:
function space(el, after) {
// defaults to a space after 4 characters:
after = after || 4;
/* removes all characters in the value that aren't a number,
or in the range from A to Z (uppercase): */
var v = el.value.replace(/[^\dA-Z]/g, ''),
/* creating the regular expression, to allow for the 'after' variable
to be used/changed: */
reg = new RegExp(".{" + after + "}","g")
el.value = v.replace(reg, function (a, b, c) {
return a + ' ';
});
}
var el = document.getElementById('iban');
el.addEventListener('keyup', function () {
space(this, 4);
});
JS Fiddle demo.
Somewhat belatedly, my rewrite of the above to handle strings, rather than DOM nodes:
function space(str, after) {
if (!str) {
return false;
}
after = after || 4;
var v = str.replace(/[^\dA-Z]/g, ''),
reg = new RegExp(".{" + after + "}", "g");
return v.replace(reg, function (a) {
return a + ' ';
});
}
var el = document.getElementById('iban');
el.addEventListener('keyup', function () {
this.value = space(this.value, 4);
});
JS Fiddle demo.
References:
addEventListener().
JavaScript regular expressions.

I wrote a simple function extending David's function to handle the last space. Also you can specify the separator.
function spacify(str, after, c) {
if (!str) {
return false;
}
after = after || 4;
c = c || " ";
var v = str.replace(/[^\dA-Z]/g, ''),
reg = new RegExp(".{" + after + "}", "g");
return v.replace(reg, function (a) {
return a + c;
}).replace(/[^0-9]+$/, "");
}
console.log(spacify("123123123131",4," "))
console.log(spacify("12312312313",4,"-"))

The code from Josh Crozie is really nice, but not complete.
Two issues with it;
If the caret is not at the end but e.g. at the before last position and the user starts typing, sometimes the caret doesn't stay at the before last position
Another issue is with Android 7+ devices. Those devices update the caret position slightly later, that means it needs a setTimeout() before reading the caret location
The code below is based on the code of Josh Crozie, now with the two issues mentioned above fixed and a little more verbose for readability purpose:
var isAndroid = navigator.userAgent.indexOf("ndroid") > -1;
var element = document.getElementById('iban');
element.addEventListener('input', function () {
if (isAndroid) {
// For android 7+ the update of the cursor location is a little bit behind, hence the little delay.
setTimeout(reformatInputField);
return;
}
reformatInputField();
});
function reformatInputField() {
function format(value) {
return value.replace(/[^\dA-Z]/gi, '')
.toUpperCase()
.replace(/(.{4})/g, '$1 ')
.trim();
}
function countSpaces(text) {
var spaces = text.match(/(\s+)/g);
return spaces ? spaces.length : 0;
}
var position = element.selectionEnd;
var previousValue = element.value;
element.value = format(element.value);
if (position !== element.value.length) {
var beforeCaret = previousValue.substr(0, position);
var countPrevious = countSpaces(beforeCaret);
var countCurrent = countSpaces(format(beforeCaret));
element.selectionEnd = position + (countCurrent - countPrevious);
}
}
<label for="iban">iban</label>
<input id="iban" type="text" name="iban" size="35" />

You have to capture each group of 4 digits and then put a space between each group.
$('input').blur(function () {
//Replace each group 4 digits with a group plus a space
var reformat = this.value.replace(/(\d{4})/g, function(match){
return match + " ";
});
this.value = reformat;
})
And this one updates the element while typing
//Keys pressed 0 times
var downed = 0;
$('#test').keydown(function (g) {
if(g.code.match("^Digit")){
downed++;
console.log(g)
}
if(downed == 1){
var reformat = this.value.replace(/(\d{4}\s*)/g, function(match){
//Strip spaces
if(match.match(/\s/)){return match;}
return match + " ";
});
console.log(reformat);
this.value = reformat;
//Start recount
downed = 0;
}
});
Check out the fiddle

for thousands on angular 4 in a pipe
integer = integer.replace(/[^\dA-Z]/g, '').replace(/(.{3})/g, '$1.').trim();

I need the same but for BVR/BVR+ swiss payment form.
So what I need is add a space every 5 chars but from the end of the string.
Example : "52 86571 22001 00000 10520 15992" or sometimes shorter like "843 14293 10520 15992".
So, here is the solution by reversing the string before and after adding spaces if rev=1.
function space(str, stp, rev) {
if (!str) {
return false;
}
if (rev == 1) {
str = str.split('').reverse().join('');
}
if(stp > 0) {
var v = str.replace(/[^\dA-Z]/g, ''),
reg = new RegExp(".{" + stp + "}", "g");
str = v.replace(reg, function (a) {
return a + ' ';
});
}
if (rev == 1) {
str = str.split('').reverse().join('');
}
return str;
}
Use :
var refTxt = space(refNum, 5, 1);
EDIT : PHP version added
function space($str=false, $stp=0, $rev= false) {
if(!$str)
return false;
if($rev)
return trim(strrev(chunk_split(strrev($str), $stp, ' ')));
else
return trim(chunk_split($str, $stp, ' '));
}

document.getElementById('iban').addEventListener('input', function (e) {
e.target.value = e.target.value.replace(/[^\dA-Z]/g, '').replace(/(.{4})/g, '$1 ').trim();
});
<label for="iban">iban</label>
<input id="iban" type="text" name="iban" />

This is the shortest version using JQuery on input with type number or tel:
$('input[type=number], input[type=tel]').on('input', function (e) {
e.target.value = e.target.value.replace(/[^\dA-Z]/g, '').replace(/(.{4})/g, '$1 ').trim();
});
You can also change the 4 to any other character limit you want.

onChangeText={number => {
const data =
number.length % 5 !== 4
? number
.replace(/[^\dA-Z]/g, '')
.replace(/(.{4})/g, '$1-')
.trim()
: number;
this.setState({
...this.state,
card: {...this.state.card, number: data},
});
}}
If you are trying to use for text input to adjust with credit card then this method will help you solve the backspace problem too

To Add space after 4 Digits
Useful to validate IBAN Number
document.getElementById('IBAN').addEventListener('input', function (e) {
e.target.value = e.target.value.replace(/[^\dA-Z]/g, '').replace(/(.{4})/g, '$1 ').trim();
});
<label for="IBAN">IBAN</label>
<input id="IBAN" maxlength="14" type="text" name="IBAN" />

struggling with creating asterisks in Javascript

I've been struggling with this for some time now. What I wanted to create is to output a triangle of asterisks based on user's input. Let say user entered size 5, it would look something like this:
*
**
***
****
*****
My HTML looks like:
<p>
Size: <input type="text" id="size">
<input type="button" value="Draw" onclick="draw()">
</p>
<pre id="output">
</pre>
In my Javascript, I have:
function draw()
{
var size = customJS.get ( "size" ); //I have a custom library where it get the Id from HTML
var theTriangle = makeTriangle( size.value ); //sending in the size
customJS.set ("output", theTriangle); //will set theTriangle to display to "output" in HTML
}
function makeTriangle( theSize )
{
var allLines = ""; // an empty string to hold the entire triangle
for ( var i = 0; i <= size; i++) // this loop size times
{
var oneLine = createLine ( i <= size ); // amount of asterisks for this line
allLines += oneLine;
}
return allLines;
}
function createLine ( length )
{
var aLine = ""; // an empty string to hold the contents of this one line
for ( var j = 0; j <= i; j++ ) //this loop length times
{
aLine += '*';
}
return aLine + "<br>";
}
anyone have any tip on how I go about this? thank you so much!

Newlines in HTML normally display as spaces, but you want them to show as newlines. The pre tag makes newlines actually appear as new lines, so wrap the output in a pre tag:
customJS.set ("output", "<pre>" + theTriangle + "</pre>");
Also, you're calling createLine like this:
var oneLine = createLine ( i <= size );
i <= size yields a boolean (true or false) rather than a number. You probably mean to just pass it i:
var oneLine = createLine ( i );
Additionally, you're setting size like this:
var size = customJS.get = ( "size" );
You probably want to drop the second equals, since as is, it sets the variable size to the string "size".
And finally, you've got a few variables wrong: in makeTriangle, you're looping size times, but size is undefined; you probably meant theSize. In createLine, you're looping i times, but i is undefined; you probably meant length.
With all that, it works.

There were several bugs in your code. For example using theSize instead size as parameter in the function makeTriangle(), using i instead of length in the createLine() function in the for loop condition.
Another one was:
use
return aLine + "<br/>";
instead of
return aLine + "\n";
The working solution for your code can be found in this jsFiddle: http://jsfiddle.net/uwe_guenther/wavDH/
And below is a copy of the fiddle:
index.html
<!DOCTYPE html>
<html>
<head>
<title></title>
</head>
<body>
<p>Size:
<input type="text" id="sizeTextField">
<input id='drawButton' type="button" value="Draw">
<div id='output'></div>
</p>
<script src='main.js'></script>
</body>
</html>
main.js
(function (document) {
var drawButton = document.getElementById('drawButton'),
sizeTextField = document.getElementById('sizeTextField'),
output = document.getElementById('output');
function makeTriangle(size) {
var allLines = '';
for (var i = 0; i <= size; i++) {
var oneLine = createLine(i); // amount of asterisks for this line
allLines += oneLine;
}
return allLines;
}
function createLine(length) {
var aLine = '';
for (var j = 0; j <= length; j++) {
aLine += '*';
}
return aLine + "<br/>";
}
drawButton.onclick = function () {
output.innerHTML = makeTriangle(sizeTextField.value);
};
})(document);

You can leverage some JavaScript tricks to make the code a bit more terse:
<div style="text-align: center">
<label>Size:
<input type="text" id="size" value="5">
</label> <pre id='output'></pre>
</div>
<script>
var size = document.getElementById('size'),
output = document.getElementById('output');
function update() {
var width = +size.value, // Coerce to integer.
upsideDown = width < 0, // Check if negative.
width = Math.abs(width), // Ensure positive.
treeArray = Array(width).join('0').split('0') // Create an array of 0s "width" long.
.map(function(zero, level) { // Visit each one, giving us the chance to change it.
return Array(2 + level).join('*'); // Create a string of *s.
});
upsideDown && treeArray.reverse(); // If width was negative, stand the tree on its head.
output.innerHTML = treeArray.join('\n'); // Join it all together, and output it!
}
size.onkeyup = update;
update();
size.focus();
</script>
http://jsfiddle.net/mhtKY/4/

Count textarea characters

I am developing a character count for my textarea on this website. Right now, it says NaN because it seems to not find the length of how many characters are in the field, which at the beginning is 0, so the number should be 500. In the console in chrome developer tools, no error occur. All of my code is on the site, I even tried to use jQuery an regular JavaScript for the character count for the textarea field, but nothing seems to work.
Please tell me what I am doing wrong in both the jQuery and the JavaScript code I have in my contact.js file.
$(document).ready(function() {
var tel1 = document.forms["form"].elements.tel1;
var tel2 = document.forms["form"].elements.tel2;
var textarea = document.forms["form"].elements.textarea;
var clock = document.getElementById("clock");
var count = document.getElementById("count");
tel1.addEventListener("keyup", function (e){
checkTel(tel1.value, tel2);
});
tel2.addEventListener("keyup", function (e){
checkTel(tel2.value, tel3);
});
/*$("#textarea").keyup(function(){
var length = textarea.length;
console.log(length);
var charactersLeft = 500 - length;
console.log(charactersLeft);
count.innerHTML = "Characters left: " + charactersLeft;
console.log("Characters left: " + charactersLeft);
});​*/
textarea.addEventListener("keypress", textareaLengthCheck(textarea), false);
});
function checkTel(input, nextField) {
if (input.length == 3) {
nextField.focus();
} else if (input.length > 0) {
clock.style.display = "block";
}
}
function textareaLengthCheck(textarea) {
var length = textarea.length;
var charactersLeft = 500 - length;
count.innerHTML = "Characters left: " + charactersLeft;
}

$("#textarea").keyup(function(){
$("#count").text($(this).val().length);
});
The above will do what you want. If you want to do a count down then change it to this:
$("#textarea").keyup(function(){
$("#count").text("Characters left: " + (500 - $(this).val().length));
});
Alternatively, you can accomplish the same thing without jQuery using the following code. (Thanks #Niet)
document.getElementById('textarea').onkeyup = function () {
document.getElementById('count').innerHTML = "Characters left: " + (500 - this.value.length);
};

⚠️ The accepted solution is outdated.
Here are two scenarios where the keyup event will not get fired:
The user drags text into the textarea.
The user copy-paste text in the textarea with a right click (contextual menu).
Use the HTML5 input event instead for a more robust solution:
<textarea maxlength='140'></textarea>
JavaScript (demo):
const textarea = document.querySelector("textarea");
textarea.addEventListener("input", event => {
const target = event.currentTarget;
const maxLength = target.getAttribute("maxlength");
const currentLength = target.value.length;
if (currentLength >= maxLength) {
return console.log("You have reached the maximum number of characters.");
}
console.log(`${maxLength - currentLength} chars left`);
});
And if you absolutely want to use jQuery:
$('textarea').on("input", function(){
var maxlength = $(this).attr("maxlength");
var currentLength = $(this).val().length;
if( currentLength >= maxlength ){
console.log("You have reached the maximum number of characters.");
}else{
console.log(maxlength - currentLength + " chars left");
}
});

textarea.addEventListener("keypress", textareaLengthCheck(textarea), false);
You are calling textareaLengthCheck and then assigning its return value to the event listener. This is why it doesn't update or do anything after loading. Try this:
textarea.addEventListener("keypress",textareaLengthCheck,false);
Aside from that:
var length = textarea.length;
textarea is the actual textarea, not the value. Try this instead:
var length = textarea.value.length;
Combined with the previous suggestion, your function should be:
function textareaLengthCheck() {
var length = this.value.length;
// rest of code
};

Here is simple code. Hope it help you
$(document).ready(function() {
var text_max = 99;
$('#textarea_feedback').html(text_max + ' characters remaining');
$('#textarea').keyup(function() {
var text_length = $('#textarea').val().length;
var text_remaining = text_max - text_length;
$('#textarea_feedback').html(text_remaining + ' characters remaining');
});
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<textarea id="textarea" rows="8" cols="30" maxlength="99" ></textarea>
<div id="textarea_feedback"></div>

This code gets the maximum value from the maxlength attribute of the textarea and decreases the value as the user types.
<DEMO>
var el_t = document.getElementById('textarea');
var length = el_t.getAttribute("maxlength");
var el_c = document.getElementById('count');
el_c.innerHTML = length;
el_t.onkeyup = function () {
document.getElementById('count').innerHTML = (length - this.value.length);
};
<textarea id="textarea" name="text"
maxlength="500"></textarea>
<span id="count"></span>

I found that the accepted answer didn't exactly work with textareas for reasons noted in Chrome counts characters wrong in textarea with maxlength attribute because of newline and carriage return characters, which is important if you need to know how much space would be taken up when storing the information in a database. Also, the use of keyup is depreciated because of drag-and-drop and pasting text from the clipboard, which is why I used the input and propertychange events. The following takes newline characters into account and accurately calculates the length of a textarea.
$(function() {
$("#myTextArea").on("input propertychange", function(event) {
var curlen = $(this).val().replace(/\r(?!\n)|\n(?!\r)/g, "\r\n").length;
$("#counter").html(curlen);
});
});
$("#counter").text($("#myTextArea").val().replace(/\r(?!\n)|\n(?!\r)/g, "\r\n").length);
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<textarea id="myTextArea"></textarea><br>
Size: <span id="counter" />

For those wanting a simple solution without jQuery, here's a way.
textarea and message container to put in your form:
<textarea onKeyUp="count_it()" id="text" name="text"></textarea>
Length <span id="counter"></span>
JavaScript:
<script>
function count_it() {
document.getElementById('counter').innerHTML = document.getElementById('text').value.length;
}
count_it();
</script>
The script counts the characters initially and then for every keystroke and puts the number in the counter span.
Martin

They say IE has issues with the input event but other than that, the solution is rather straightforward.
ta = document.querySelector("textarea");
count = document.querySelector("label");
ta.addEventListener("input", function (e) {
count.innerHTML = this.value.length;
});
<textarea id="my-textarea" rows="4" cols="50" maxlength="10">
</textarea>
<label for="my-textarea"></label>

var maxchar = 10;
$('#message').after('<span id="count" class="counter"></span>');
$('#count').html(maxchar+' of '+maxchar);
$('#message').attr('maxlength', maxchar);
$('#message').parent().addClass('wrap-text');
$('#message').on("keydown", function(e){
var len = $('#message').val().length;
if (len >= maxchar && e.keyCode != 8)
e.preventDefault();
else if(len <= maxchar && e.keyCode == 8){
if(len <= maxchar && len != 0)
$('#count').html(maxchar+' of '+(maxchar - len +1));
else if(len == 0)
$('#count').html(maxchar+' of '+(maxchar - len));
}else
$('#count').html(maxchar+' of '+(maxchar - len-1));
})
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<textarea id="message" name="text"></textarea>

$(document).ready(function(){
$('#characterLeft').text('140 characters left');
$('#message').keydown(function () {
var max = 140;
var len = $(this).val().length;
if (len >= max) {
$('#characterLeft').text('You have reached the limit');
$('#characterLeft').addClass('red');
$('#btnSubmit').addClass('disabled');
}
else {
var ch = max - len;
$('#characterLeft').text(ch + ' characters left');
$('#btnSubmit').removeClass('disabled');
$('#characterLeft').removeClass('red');
}
});
});

This solution will respond to keyboard and mouse events, and apply to initial text.
$(document).ready(function () {
$('textarea').bind('input propertychange', function () {
atualizaTextoContador($(this));
});
$('textarea').each(function () {
atualizaTextoContador($(this));
});
});
function atualizaTextoContador(textarea) {
var spanContador = textarea.next('span.contador');
var maxlength = textarea.attr('maxlength');
if (!spanContador || !maxlength)
return;
var numCaracteres = textarea.val().length;
spanContador.html(numCaracteres + ' / ' + maxlength);
}
span.contador {
display: block;
margin-top: -20px;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<textarea maxlength="100" rows="4">initial text</textarea>
<span class="contador"></span>

Using Regex to limit special characters in a textbox using jquery in ASP.net MVC form

I'm trying to limit to 3 the number of special characters in a text box using JQuery. The special characters can be in any order and can be adjacent to each other or scattered over the length of the text box. I spent the last 24 hours reading almost all relevant posts in stackoverflow and trying the suggestions.
I still haven't come with a suitable regex.
Here is what I have so far at the bottom of my ASP.net mvc form:
<script type="text/javascript">
$(document).ready(function () {
$('input[id$=textbox1]').bind('blur', function () {
var match = /^[.,:;!?€¥£¢$-~#%&*()_]{4,50}$/g.test(this.value);
if (match == true)
alert("Please enter a maximum of 3 special characters.");
});
});
</script>
Below is the list of special characters I'm targeting:
~`!##%^&*()-_:;?€¥£¢$-~{}[]<>/+|=

You where thinking to difficullty. Just count how often the elements are inside the input and throw a warning when the count is over three.
here is an
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Demo</title>
<script src="jquery-1.8.3.min.js"></script>
<script>
var limitchars = '[~`!##%\^&\*\(\)-_:;\?€¥£¢\${}\[]<>/+\|=]'
$(function () {
var teststring = "~`!##%\^&\*\(\)-_:;\?€¥£¢\${}\[]<>/+\|='-:;";
var regex = /[~`'!##%\^&\*\(\)-_:;\?€¥£¢\${}\[\]<>/+\|=]/g
//var test1 = teststring.match(regex);
//debugger;
//alert(teststring.length === test1.length);
$('input').keyup(function () {
var text = this.value;
var match = text.match(regex);
if (match.length > 3) {
alert('invalidI input');
}
});
});
</script>
</head>
<body>
<input type="text" />
</body>
</html>
Don't forget to escape the regular expression (http://www.regular-expressions.info/reference.html ). The g at the end of the regex counts the number of occurrence in string (http://stackoverflow.com/questions/4009756/how-to-count-string-occurrence-in-string )

You can find the number of bad characters by counting the number of matches.
Working example at http://jsbin.com/alidus/1/
$(document).ready(function () {
$('#test').bind('blur', function () {
var charactersToExlude = "~`!##%^&*()-_:;?€¥£¢$-~{}[]<>/+|=";
var badCharacterRegex = "[" + charactersToExlude.replace(/[\-\[\]{}()*+?.,\\\^$|#\s]/g, "\\$&") + "]";
console.log(badCharacterRegex);
var patt=new RegExp(badCharacterRegex, "g");
var matches = this.value.match(patt);
var numberOfBadCharacters = matches ? matches.length : 0;
if (numberOfBadCharacters >= 3) {
$("#result").text("Please enter a maximum of 3 special characters. (" + numberOfBadCharacters + " bad characters).");
} else {
$("#result").text(numberOfBadCharacters + " bad characters.");
}
});
});
First we escape any bad characters that have meaning to regex. Then crete the pattern, match it, if any matches, count the number of matches.

$(document).ready(function () {
$('#test').bind('blur', function () {
var charactersToExlude = "~`!##%^&*()-_:;?€¥£¢$-~{}[]<>/+|=";
var badCharacterRegex = "[" + charactersToExlude.replace(/[\-\[\]{}()*+?.,\\\^$|#\s]/g, "\\$&") + "]";
console.log(badCharacterRegex);
var patt=new RegExp(badCharacterRegex, "g");
var matches = this.value.match(patt);
var numberOfBadCharacters = matches ? matches.length : 0;
if (numberOfBadCharacters >= 3) {
$("#result").text("Please enter a maximum of 3 special characters. (" + numberOfBadCharacters + " bad characters).");
} else {
$("#result").text(numberOfBadCharacters + " bad characters.");
}
});
});