Answer: edit out anything you dont need
<!DOCTYPE html>
<html lang = "en">
<head>
<title> JavaScript Calculator </title>
<style>
h1 {
text-align: center;
padding: 23px;
background-color: skyblue;
color: white;
}
#clear{
width: 270px;
border: 3px solid gray;
border-radius: 3px;
padding: 20px;
background-color: red;
}
.formstyle
{
width: 300px;
height: 530px;
margin: auto;
border: 3px solid skyblue;
border-radius: 5px;
padding: 20px;
}
input
{
width: 20px;
background-color: green;
color: white;
border: 3px solid gray;
border-radius: 5px;
padding: 26px;
margin: 5px;
font-size: 15px;
}
#calc{
width: 250px;
border: 5px solid black;
border-radius: 3px;
padding: 20px;
margin: auto;
}
</style>
</head>
<body>
<h1> Calculator Program in JavaScript </h1>
<div class= "formstyle">
<form name = "form1">
<!-- This input box shows the button pressed by the user in calculator. -->
<input id = "calc" type ="text" name = "answer"> <br> <br>
<!-- Display the calculator button on the screen. -->
<!-- onclick() function display the number prsses by the user. -->
<input type = "button" value = "1" onclick = "form1.answer.value += '1' ">
<input type = "button" value = "2" onclick = "form1.answer.value += '2' ">
<input type = "button" value = "3" onclick = "form1.answer.value += '3' ">
<input type = "button" value = "+" onclick = "form1.answer.value += '+' ">
<br> <br>
<input type = "button" value = "4" onclick = "form1.answer.value += '4' ">
<input type = "button" value = "5" onclick = "form1.answer.value += '5' ">
<input type = "button" value = "6" onclick = "form1.answer.value += '6' ">
<input type = "button" value = "-" onclick = "form1.answer.value += '-' ">
<br> <br>
<input type = "button" value = "7" onclick = "form1.answer.value += '7' ">
<input type = "button" value = "8" onclick = "form1.answer.value += '8' ">
<input type = "button" value = "9" onclick = "form1.answer.value += '9' ">
<input type = "button" value = "*" onclick = "form1.answer.value += '*' ">
<br> <br>
<input type = "button" value = "/" onclick = "form1.answer.value += '/' ">
<input type = "button" value = "0" onclick = "form1.answer.value += '0' ">
<input type = "button" value = "." onclick = "form1.answer.value += '.' ">
<!-- When we click on the '=' button, the onclick() shows the sum results on the calculator screen. -->
<input type = "button" value = "=" onclick = "form1.answer.value = eval(form1.answer.value) ">
<br>
<!-- Display the Cancel button and erase all data entered by the user. -->
<input type = "button" value = "Clear All" onclick = "form1.answer.value = ' ' " id= "clear" >
<br>
</form>
</div>
</body>
</html>
Explanation: