Делаете калькулятор, используя события?

Question

Я пытаюсь сделать калькулятор в JavaScript с использованием только ограниченного HTML. У меня было много проблем с этим, потому что я не очень хорошо это понимал. До сих пор мой калькулятор был раскрашен в Javascript и может выполнять вычисления в консоли.

У меня есть вопросы:

1. Как бы я отобразил предупреждение «Пожалуйста, введите значение», если пользователь нажал кнопку = , когда ничего не отображается Кнопки MS , M C и MR .

2. И Очистите дисплей, нажав C (очистить) кнопка

Больше всего мне хотелось бы решить, как сделать так, чтобы числа отображались на черном экране калькулятора.

//3.
//Changing colors of opertion colors 

//Multiply Color
const colorMultiply = document.getElementById('multiply')
colorMultiply.style.backgroundColor = "green" //Makes Color Green

//Divide Color
const colorDivide = document.getElementById('divide')
colorDivide.style.backgroundColor = "red" //Makes Color Red

//subtract color
const colorSubtract = document.getElementById('subtract')
colorSubtract.style.backgroundColor = "blue" //Makes Color Blue

//add color
const colorAdd = document.getElementById('add')
colorAdd.style.backgroundColor = "yellow" //Makes Color Yellow


//change font of numbers to blue (I did it like this incase anyone wants to color of a single number)
//Makes it easier for you to change a colour of one button
const number1 = document.getElementById('number1')
number1.style.color = "blue"
const number2 = document.getElementById('number2')
number2.style.color = "blue"
const number3 = document.getElementById('number3')
number3.style.color = "blue"
const number4 = document.getElementById('number4')
number4.style.color = "blue"
const number5 = document.getElementById('number5')
number5.style.color = "blue"
const number6 = document.getElementById('number6')
number6.style.color = "blue"
const number7 = document.getElementById('number7')
number7.style.color = "blue"
const number8 = document.getElementById('number8')
number8.style.color = "blue"
const number9 = document.getElementById('number9')
number9.style.color = "blue"
const number0 = document.getElementById('number0')
number0.style.color = "blue"
const decimal = document.getElementById('decimal')
decimal.style.color = "blue"

//Changing color of the clear button
const clear = document.getElementById('clear')
clear.style.color = "white"
clear.style.backgroundColor = "black"

///////////////////////////////////////////////////////////////////////////////////////////////////////
// Then we want to insert `memoryStoreButton` before the `clear` button:
var memoryStoreButton = document.createElement("BUTTON");
memoryStoreButton.innerHTML = "MS";
clear.before(memoryStoreButton); //puts button before clear

// Then we want the `memoryClearButton` before `memoryStoreButton`
var memoryClearButton = document.createElement("BUTTON");
memoryClearButton.innerHTML = "MC";
memoryStoreButton.before(memoryClearButton); //puts button before clear

// and finally, the `memoryRestoreButton` before `memoryClearButton`
var memoryRestoreButton = document.createElement("BUTTON");
memoryRestoreButton.innerHTML = "MR";
memoryClearButton.before(memoryRestoreButton); //puts button before clear

///////////////////////////////////////////////////////////////////////////////////////////////////////////
//What buttons are pressed
var expression = [];

document.querySelector(".buttons8").onclick = function(e) {
  if (e.target.nodeName === "BUTTON") {
    if (e.target.innerHTML !== "=") {
      expression.push(e.target.innerHTML);
    } else {
      console.log(eval(expression.join("")));
      expression = [];
    }
  }
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
}

.calculator8 {
  flex: 0 0 40%;
}

.screen8 {
  width: 100%;
  font-size: 7rem;
  padding: 0.5rem;
  background: rgb(41, 41, 56);
  color: white;
  border: none;
}

.buttons8 {
  display: flex;
  flex-wrap: wrap;
  transition: all 0.5s linear;
}

button {
  flex: 0 0 25%;
  border: 1px solid black;
  padding: 0.25rem 0;
  transition: all 2s ease;
}

.btn-kground: rgb(224, 224, 224);

}
.btn8 {
  font-size: 4rem;
}

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">

  <title> Calculator 8 </title>
  <script src="fp.js" defer></script>
  <link rel="stylesheet" href="fp.css">



</head>

<body>
  <section class="calculator8">
    <h1> Calculator 8 </h1>
    <form>
      <input type="text" name="" id="numberBox" class="screen8">
    </form>
    <div class="buttons8">
      <!-- operation buttons -->
      <button id="multiply" type="button" class="btn8 btn-mul" data-num="*">*</button>
      <button id="divide" type="button" class="btn8 btn-div" data-num="/">/</button>
      <button id="subtract" type="button" class="btn8 btn-sub" data-num="-">-</button>
      <button id="add" type="button" class="btn8 btn-add" data-num="+">+</button>
      <!-- number buttons -->
      <button id="decimal" type="button" class="btn8 btn-grey" data-num=".">.</button>
      <button id="number9" type="button" class="btn8 btn-grey" data-num="9">9</button>
      <button id="number8" type="button" class="btn8 btn-grey" data-num="8">8</button>
      <button id="number7" type="button" class="btn8 btn-grey" data-num="7">7</button>
      <button id="number6" type="button" class="btn8 btn-grey" data-num="6">6</button>
      <button id="number5" type="button" class="btn8 btn-grey" data-num="5">5</button>
      <button id="number4" type="button" class="btn8 btn-grey" data-num="4">4</button>
      <button id="number3" type="button" class="btn8 btn-grey" data-num="3">3</button>
      <button id="number2" type="button" class="btn8 btn-grey" data-num="2">2</button>
      <button id="number1" type="button" class="btn8 btn-grey" data-num="1">1</button>
      <button id="number0" type="button" class="btn8 btn-grey" data-num="0">0</button>
      <button id="equals" type="button" class="btn8 btn-grey">=</button>
      <button id="clear" type="button" class="btn8 btn-grey">C</button>


    </div>



  </section>


</body>

</html>