If you're doing this to several fields, or doing it quite often, then perhaps a plugin is the answer.
Here's the beginnings of a jQuery plugin that formats the value of a field to two decimal places.
It is triggered by the onchange event of the field. You may want something different.

<script type="text/javascript">

    // mini jQuery plugin that formats to two decimal places
    (function($) {
        $.fn.currencyFormat = function() {
            this.each( function( i ) {
                $(this).change( function( e ){
                    if( isNaN( parseFloat( this.value ) ) ) return;
                    this.value = parseFloat(this.value).toFixed(2);
                });
            });
            return this; //for chaining
        }
    })( jQuery );

    // apply the currencyFormat behaviour to elements with 'currency' as their class
    $( function() {
        $('.currency').currencyFormat();
    });

</script>   
<input type="text" name="one" class="currency"><br>
<input type="text" name="two" class="currency">

This requires two operations...

1. Parse the number string into a Number instance

   const actualNumber = +number.replace(/,/g, '') // produces 4500.02734
   

2. Format the string to a given locale with a maximum of 2 decimal places

   const formatted = actualNumber.toLocaleString('en-US', {maximumFractionDigits: 2})
   

var number = '4,500.02734'

const actualNumber = +number.replace(/,/g, '')
const formatted = actualNumber.toLocaleString('en-US', {maximumFractionDigits: 2})

document.write(formatted)

@cane van caneYou can limit it via regex and JavaScript combination. Eliminate the ‘,’ input and limit number from 2-10 along with decimal places (below code limits to 2 digits after decimal). If the input doesn’t match regex it would clear the text box. Add below code in Question JavaScript section.Qualtrics.SurveyEngine.addOnload(function() { var inputElement = jQuery("#" + this.questionId + " .InputText"); inputElement.on("blur", function() { var inputValue = jQuery(this).val(); // Regex for valid number format (2-9.99 or 10) var numberPattern = /^((10)|(2-9?))$/; if (!numberPattern.test(inputValue)) { // Invalid input jQuery(this).val(""); // Clear the input field or handle as needed } });});Hope it helps!Happy Holidays

$(this).temp1() looks particularly out of place, I think you just meant to use the temp1 variable. Since it's already a number, you don't need to use parseFloat on it either:

$("#discount").change(function() {
    var list = $("#list").val();
    var discount = $("#discount").val();
    var price = $("#price");
    var temp = discount * list;
    var temp1 = list - temp;
    var total = temp1.toFixed(2);

    price.val(total);
});

Did you add the locale to the toLocaleString function? for example javascript var number = 12345.543; number.toLocaleString('en') if i print the above code in the console it shows "12,345.543"

(Math.round(num * 100) / 100).toFixed(2);

Live Demo

var num1 = "1";
document.getElementById('num1').innerHTML = (Math.round(num1 * 100) / 100).toFixed(2);

var num2 = "1.341";
document.getElementById('num2').innerHTML = (Math.round(num2 * 100) / 100).toFixed(2);

var num3 = "1.345";
document.getElementById('num3').innerHTML = (Math.round(num3 * 100) / 100).toFixed(2);

span {
    border: 1px solid #000;
    margin: 5px;
    padding: 5px;
}

<span id="num1"></span>
<span id="num2"></span>
<span id="num3"></span>

Note that it will round to 2 decimal places, so the input 1.346 will return 1.35.

This seems to work

var formatNumber = function(num) {
    return parseFloat(num).toFixed(2).toLocaleString();
};

You need to use the .toFixed() method

It takes as a parameter the number of digits to show after the decimal point.

$(document).ready(function() {
  $('.add').click(function() {
     var value = parseFloat($('#total').text()) + parseFloat($(this).data('amount'))/100
     $('#total').text( value.toFixed(2) );
  });
})