JavaScript

$("#closing-time").keyup(function(){

$(function(){ 
$("#closing-time").keyup(function(){
	var openingTime = $("#openingTime").val();
	var closingTime = $("#closingTime").val();
     $("hoursOpen").html(closingTime-openingTime);
	return hoursOpen.html;

$("hoursOpen")

$("#hoursOpen")

$(function(){
    // Convert either "HH.mm" or "HH:mm" to the number of minutes since midnight
    var parseMinutes = function(value){
        var parts = value.split(/[.:]/g);
        switch (parts.length) {
            case 1: {
                return parseFloat(parts[0]) * 60;
            }
            case 2: {
                var hours = parseFloat(parts[0]);
                var minutes = parseFloat(parts[1]);
                return (hours * 60) + minutes;
            }
            default: {
                return 0;
            }
        }
    };
    
    // Format a number of minutes as "HH:mm"
    var formatMinutes = function(minutes){
        var hours = Math.floor(minutes / 60);
        minutes %= 60;
        
        return hours.toString().padStart(2, '0') + ':' + minutes.toString().padStart(2, '0');
    };
    
    var updateHoursOpen = function(){
        var openingTime = $("#opening-time").val();
        var closingTime = $("#closing-time").val();
        
        var openingMinutes = parseMinutes(openingTime);
        var closingMinutes = parseMinutes(closingTime);
        var minutesOpen = closingMinutes - openingMinutes;
        
        // If closing is before opening, the time spans midnight. Add a day's worth of minutes:
        if (minutesOpen < 0) {
            minutesOpen += 1440;
        }
        
        var hoursOpen = formatMinutes(minutesOpen);
        $("#hoursOpen").val(hoursOpen);
        return hoursOpen;
    };
    
    // Update the hours when either input is changed:
    $("#opening-time, #closing-time").keyup(updateHoursOpen);
});

<div class="opening-day">
    <p>Monday</p>
    <p>
        <label>
            Opening:
            <input type='text' class='opening-time' value='00:00'>
        </label>
    </p>
    <p>
        <label>
            Closing:
            <input type='text' class='closing-time' value='00:00'>
        </label>
    </p>
    <p>
        Result:
        <input type='text' class='hours-open' value='00:00' readonly>
    </p>
</div>

var updateHoursOpen = function($div){
    var openingTime = $div.find(".opening-time").val();
    var closingTime = $div.find(".closing-time").val();
    
    var openingMinutes = parseMinutes(openingTime);
    var closingMinutes = parseMinutes(closingTime);
    var minutesOpen = closingMinutes - openingMinutes;
    if (minutesOpen < 0) {
        minutesOpen += 1440;
    }
    
    var hoursOpen = formatMinutes(minutesOpen);
    $div.find(".hours-open").val(hoursOpen);
    return hoursOpen;
};

$(".opening-day").on("keyup", ".openingtime, .closing-time", function(){
    var $div = $(this).closest(".opening-day");
    updateHoursOpen($div);
});

setStoreHours(): void {
    const date = new Date();
    const newDate = new Date(date.getTime() + date.getTimezoneOffset() * 60 * 1000);
    const offset = date.getTimezoneOffset() / 60;
    this.hourOfDay = date.getHours();
    this.dayOfWeek = date.getDay();
    switch (this.dayOfWeek) {
      case 0:
        // Sunday
        this.storeStatus = "Closed";
        break;
      case 1:
        // Monday
        if (this.hourOfDay > 8 && this.hourOfDay < 17) {
          this.storeStatus = "Open";
        }
        break;
      case 2:
        // Tuesday
        if (this.hourOfDay > 8 && this.hourOfDay < 17) {
          this.storeStatus = "Open";
        }
        break;
      case 3:
        // Wednesday
        if (this.hourOfDay > 8 && this.hourOfDay < 17) {
          this.storeStatus = "Open";
        }
        break;
      case 4:
        // Thursday
        if (this.hourOfDay > 8 && this.hourOfDay < 17) {
          this.storeStatus = "Open";
        }
        break;
      case 5:
        // Friday
        if (this.hourOfDay > 8 && this.hourOfDay < 15) {
          this.storeStatus = "Open";
        }
        break;
      case 6:
        // Saturday
        this.storeStatus = "Closed";
        break;
      default:
        this.storeStatus = "Closed";
    }
  }

<button type="button" onBlur="calcTime()">Calculate</button>

function calcTime() {

  // Make references to input elements
  const time = document.getElementById("currentCharge"),
    current = document.getElementById("timeAllowed"),
    breakEven = document.getElementById("breakEven");

  // Get the element values, convert to number/float
  // By default, values are strings, and don't do math well.
  let t = parseFloat(time.value);
  let c = parseFloat(current.value);

  // Perform the equation
  let bE = t * c;

  // Output the equation
  breakEven.innerHTML = bE.toString();

}