jQuery - JavaScript regex allow only numeric and minus sign as first character

Question

I want users to enter numeric values only in my input hence I put below code.

<input type="text" class="form-control rounded-pill bg-light" autocomplete="off" name="free_credit_amount" id="free_credit_amount" placeholder="Free credit amount">

$('body').on('keyup', '#free_credit_amount', function(){
    this.value = this.value.replace(/[^0-9\.]/g,'');
});

This is working fine for me .. however I have a requirement that, users can enter negative values as well .. something like -500 , hence I have updated my JavaScript Regex a bit with something like following ..

$('body').on('keyup', '#free_credit_amount', function(){   
   this.value = this.value.replace(/[^-0-9]/g,'');
});

This is also working fine for me as I am able to type minus (-) sign and can enter a value something like 500 or -500 however, I want to furnish this regex a bit .. Currently what is happening, I can also enter a value like 500-. This should not be allowed .. I only want my minus (-) to be only added as first character..

I have tried to use various other REGEX like this.value = this.value.replace(/(\+|\-)?[^-0-9]/g,''); this.value = this.value.replace(/^[-][a-zA-Z0-9.,$;]/g,'');

But none of those REGEX working for me ..

Can someone help me to achieve this plz ..

Thanks

Answer 1

You can use

$('body').on('input', '#free_credit_amount', function(){
    var position = this.selectionStart;
    var oldval = this.value;
    var newval = this.value.replace(/[^0-9.-]/g, '').replace(/^(-)|-+/g,'$1').replace(/^([^.]*\.)|\.+/g, '$1');
    this.value = newval;
    if (oldval != newval) {
        this.selectionEnd = position-1;
    }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<input type="text" class="form-control rounded-pill bg-light" autocomplete="off" name="free_credit_amount" id="free_credit_amount" placeholder="Free credit amount">

Here,

• .replace(/[^0-9.-]/g, '') - removes all chars other than digits, dots and hyphens
• .replace(/^(-)|-+/g,'$1') - keeps the hyphen at the start of the string and removes all other hyphens
• .replace(/^([^.]*\.)|\.+/g, '$1') - keeps any amount of text other than . and the first ., and removes all other dots in the string