Arithmetic expressions in Javascript

Question

I have studied java and php for many years and recently just started developing in JavaScript as well. Anyway a fairly noob question but can anyone work out why this application isn't showing displaying the interest when the button is clicked? I have been using w3schools website to learn from.

code:

<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Interest Calculator</title>
</head>
<body>

<fieldset>
<legend>Interest Calculator</legend>
Enter amount: <input type="text" id="amount" ><br><br>
Interest rate: <input type="text" id="interest"><br><br>
Enter years: <input type="text" id="years"><br><br>
<button onclick="calculate()">Calculate</button>
</fieldset>

<p id="sum"></p>

<script>

function calculate(){

var amount = document.getElementById("amount").value;
var rate = document.getElementById("interest").value;
var years = document.getElementById("years").value;
var sum = amount(1+rate)^years;

var message = "Your total return will be: " + sum;

document.getElementById("sum").innerHTML = message;


}

</script>

</body>
</html>

Many thanks,

Adam

I'll go out on a limb here, and guess it's the fact that amount is not a function, but a string ? — adeneo
– adeneo, Commented Nov 29, 2015 at 21:51
@user3918443 What you have done is amount( - That's declaring as a function. — Praveen Kumar Purushothaman
– Praveen Kumar Purushothaman, Commented Nov 29, 2015 at 22:11

Praveen Kumar Purushothaman · Accepted Answer · 2015-11-29 21:52:25Z

2

You need to explicitly specify *. It is not normal for 5(3) = 15 in JavaScript or any programming language. You need to explicitly specify 5*(3):

var sum = amount*(1+rate)^years;

Working Code

<fieldset>
  <legend>Interest Calculator</legend>
  Enter amount: <input type="text" id="amount" ><br><br>
  Interest rate: <input type="text" id="interest"><br><br>
  Enter years: <input type="text" id="years"><br><br>
  <button onclick="calculate()">Calculate</button>
</fieldset>

<p id="sum"></p>

<script>
  function calculate(){
    var amount = document.getElementById("amount").value;
    var rate = document.getElementById("interest").value;
    var years = document.getElementById("years").value;
    var sum = amount*(1+rate)^years;
    var message = "Your total return will be: " + sum;
    document.getElementById("sum").innerHTML = message;
  }
</script>

Fiddle: http://jsbin.com/lovevazaxe

answered Nov 29, 2015 at 21:52

Praveen Kumar Purushothaman

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2 Comments

user3918443 Over a year ago

I can in 3 minutes apparently :)

Praveen Kumar Purushothaman Over a year ago

Thanks @user3918443... This motivates people like us to answer questions.

Danield · Accepted Answer · 2015-11-30 09:10:54Z

0

The OP uses the ^ operator and presumably wants to use the power-of operator.

In javascript the ^ operator refers to bitwise XOR - I don't think that's what the OP wants.

Instead, the power-of operation is done with the Math.pow() function.

So replace var sum = amount(1+rate)^years; with

var sum = Math.pow(amount*(1+rate),years)

edited Nov 30, 2015 at 9:10

answered Nov 29, 2015 at 22:17

Danield

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