Using Regular Expressions for validation restricts the functionality of home, end, and arrow keys

Question

Using Regular Expressions for validation restricts the functionality of home, end, and arrow keys

Issue: My HTML text input has a script that restricts input to alphanumeric characters in the onpress, onkeydown, and onkeyup events:

this.value = this.value.replace(/[^a-zA-Z0-9]/, '')

While this validation ensures only alphanumeric characters can be entered, it also prevents normal cursor movement using keys like home, end, or arrow keys. Cursor adjustment is limited to using the backspace key, which may not always be ideal.

I am curious about why this behavior occurs specifically in Firefox and Chrome (I have not tested it in IE yet). My assumption is that it could be related to the this.value = part of the code, as regular expressions typically do not handle arrow key functionality.

javascript regex validation

Answer 1

Answer №1

When you replace the entire content with every keystroke (three times per keystroke, actually), the cursor is positioned at the end after the replacement takes place.

Instead of this method, I recommend a different approach: only replace the contents of the field if the validation does not pass:

<input id="uname" type="text">

var f = document.getElementById('uname');
f.addEventListener('keyup', function(e){
    var regex = /[^a-zA-Z0-9]/;
    if(regex.test(this.value)) {
        this.value = this.value.replace(regex, '')  
    }
});

_{To use the JavaScript snippet above, make sure to add it within a <script> tag just before </body>, or wrap it in a document.ready/DOMContentLoaded/window.onload handler to ensure the field exists when it runs.}

View Demo

Answer 2

When you replace the entire content with every keystroke (three times per keystroke, actually), the cursor is positioned at the end after the replacement takes place.

Instead of this method, I recommend a different approach: only replace the contents of the field if the validation does not pass:

<input id="uname" type="text">

var f = document.getElementById('uname');
f.addEventListener('keyup', function(e){
    var regex = /[^a-zA-Z0-9]/;
    if(regex.test(this.value)) {
        this.value = this.value.replace(regex, '')  
    }
});

_{To use the JavaScript snippet above, make sure to add it within a <script> tag just before </body>, or wrap it in a document.ready/DOMContentLoaded/window.onload handler to ensure the field exists when it runs.}

View Demo

Answer 3

Answer №2

There are a couple of points to address. Firstly, the event is being triggered thrice which appears redundant. To rectify this issue, consider implementing the following approach:

<script type="text/javascript">
    function enforceAlphaNumeric(inputField){
        var invalidCharacters = /[^a-z0-9]/ig
        if(inputField.value.match(invalidCharacters))
            inputField.value = inputField.value.replace(invalidCharacters, '');
     }
</script>
<input id="username" type="text" onkeypress="enforceAlphaNumeric(this);" />

Answer 4

There are a couple of points to address. Firstly, the event is being triggered thrice which appears redundant. To rectify this issue, consider implementing the following approach:

<script type="text/javascript">
    function enforceAlphaNumeric(inputField){
        var invalidCharacters = /[^a-z0-9]/ig
        if(inputField.value.match(invalidCharacters))
            inputField.value = inputField.value.replace(invalidCharacters, '');
     }
</script>
<input id="username" type="text" onkeypress="enforceAlphaNumeric(this);" />

Using Regular Expressions for validation restricts the functionality of home, end, and arrow keys

Answer №1

Answer №2

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