javascript functions arguments

Question

Have created a basic form, three drop down lists and a button. im tryn to multiply the three values in the down lists. i have to pass the data up to the function. i have ran the code just keep getting 0 as the result?? I don't think I'm passing the data from from up to the function correctly?

<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Untitled Document</title>
</head>

<body>
<script>
function multiply(number1, number2, number3)
{
    var firstnum=0;
    var secondnum=0;
    var thirdnum=0;
    var answer;
    firstnum=parseInt(number1);
    secondnum=parseInt(number2);
    thirdnum==parseInt(number3);
    answer=(firstnum*secondnum*thirdnum);
    alert(answer)
}

</script>

<form name="Example1">
Number 1:
<select id="num1">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
</select>
<br/>
Number 2:
<select id="num2">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
</select>
<br/>
Number 2:
<select id="num3">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
</select>
<br/>
<input type=button value="muliply" onclick="multiply(num1.value, num2.value, num3.value)" />
</form>
</body>
</html>

Please try to check the syntax is proper always...@Francis Gall — Dinesh Kanivu
– Dinesh Kanivu, Commented Oct 3, 2013 at 11:38

Quentin · Accepted Answer · 2013-10-03 11:31:29Z

Your problem is:

thirdnum==parseInt(number3); is a comparison, not an assignment, so thirdnum will always be 0.

Since you are multiplying by thirdnum, and anything × 0 is 0, you will always get 0 as the output.

Change == to =.

This would have been picked up if you had QAed your code with JS Hint.

Your bad practises which you should fix are:

num1.value assumes global JS variables will be created for every element with an id. Don't assume that, use document.getElementById
parseInt(number1) doesn't have a radix. Always specify the number system you are using (normally base 10) so it isn't inferred from the data for unexpected results: parseInt(number1, 10);
<form name="Example1">, the name attribute on forms is a legacy from before the id attribute had come around properly. Use id to identify elements for client side code.
onclick attributes do a poor job of separating concerns. Use addEventListener (or a library such as YUI or jQuery if you need to support old versions of IE).

iJade · Accepted Answer · 2013-10-03 11:30:33Z

0

OK u keep getting 0 as result because of this

thirdnum==parseInt(number3);

in your multiply function

Change it to

thirdnum=parseInt(number3);

And you should be good to go

Here is a demo

answered Oct 3, 2013 at 11:30

iJade

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