Aquí tenemos una calculadora básica de creación de JavaScript
<!DOCTYPE html>
<html>
<head>
<title>Kalkulator</title>
<meta charset="utf-8" />
<style type="text/css">
#calculator {
background: #0000FF;
margin: auto;
padding: 50px 50px 50px 50px;
width: 200px;
text-align: center;
}
#calculator button{
background: #FFEBCD;
padding: 13px;
width: 13px;
padding-right:33px;
max-width: 300px;
margin:auto;
text-align: center;
}
#calculator input[type="text"] {
padding: 20px;
width: 160px;
margin-bottom: 10px;
text-align: center;
}
</style>
<script>
function Calculator(operator)
{
var a = document.getElementById('a').value;
var b = document.getElementById('b').value;
switch(operator)
{
case '+':
var result = parseFloat(a) + parseFloat(b);
break;
case '-':
var result = parseFloat(a) - parseFloat(b);
break;
case 'x':
var result = parseFloat(a) * parseFloat(b);
break;
case '/':
var result = parseFloat(a) / parseFloat(b);
break;
case 'C':
var result = '0';
break;
case '√a':
var result = Math.pow(a, 0.5);
break;
case 'a^b':
var result = Math.pow(a, b);
break;
case '%':
var result = parseFloat(a) * parseFloat(b)/100;
break;
case 'log(a)':
var result = Math.log(a);
break;
}
document.getElementById('result').value = '= ' + result;
}
</script>
</head>
<body>
<form id="calculator">
<input type="text" id="a" placeholder="a" />
<input type="text" id="b" placeholder="b" />
<input type="text" id="result" placeholder="=" disabled="disabled" />
<p><button type="button" onclick="Calculator(this.innerHTML)">C</button>
<button type="button" onclick="Calculator(this.innerHTML)">+</button>
<button type="button" onclick="Calculator(this.innerHTML)">-</button>
<button type="button" onclick="Calculator(this.innerHTML)">x</button>
<button type="button" onclick="Calculator(this.innerHTML)">/</button>
<button type="button" onclick="Calculator(this.innerHTML)">√a</button>
<button type="button" onclick="Calculator(this.innerHTML)">a^b</button>
<button type="button" onclick="Calculator(this.innerHTML)">%</button>
<button type="button" onclick="Calculator(this.innerHTML)">log(a)</button></p>
</form>
</body>