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I'm really new to Javascript and trying to create a form where I'm running into some trouble...

When I use + it does not add up to the value, instead it just puts it back to back. Ex: 5+10 (510)

Here's my code if you want to take a look at it. I'd appreciate any help since I can't figure this out on my own.

var service = document.getElementById("service");
var serviceprice = service.options[service.selectedIndex].id;

var tech = document.getElementById("tech");
var techprice = tech.options[tech.selectedIndex].id;

var hours = document.getElementById("hours").value;

// The error happens here
var total = techprice * hours + serviceprice;

I also have an html part which the script gets the data from.

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4 Answers 4

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That happens whenever you have a string rather than a number. The + operator performs concatenation for strings. Make sure you parse your strings to numbers using parseFloat or parseInt:

var service = document.getElementById("service");
var serviceprice = parseInt(service.options[service.selectedIndex].id, 10);
var tech = document.getElementById("tech");
var techprice = parseInt(tech.options[tech.selectedIndex].id, 10);
var hours = parseInt(document.getElementById("hours").value, 10);

Note that parseInt takes an argument to specify the base. You almost always want base 10.

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6 Comments

+1 on the base 10 note. That's bitten me more than once when I've accepted leading zeros and end up with base-8 numbers.
And just to make it interesting, see this link for benchmarks comparing speed of various string to number conversions functions and methods: jsperf.com/number-vs-plus-vs-toint-vs-tofloat/13
@meewoK Cool comparison. Also a dictionary of ways to convert a string to a number.
You can also multiply your stringified numbers by 1 before adding.
@Paul Yup, there are tons of ways to convert a number, but many of them work slightly different with certain strings. meewoK's perf has a whole bunch of ways to do the conversion.
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Try changing this line:

var total = techprice * hours + serviceprice;

to

var total = techprice * hours + parseFloat(serviceprice);

I suspect 'servicePrice' is a string, and it will then try to concatenate the first value (let's say: 100) with the second value (which is, not a number, but a string, let's say 'test'), the result being '100test'.

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Try to convert the string to int first with parseInt or to float with parseFloat

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This is not especially elegant, but I find it simple, easy, and useful:

var total = -(-techprice * hours - serviceprice);

or even:

var total = techprice * hours -(-serviceprice);

They both eliminate the ambiguous + operator.

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2 Comments

I do not think he wants to eliminate and remove the + operator . He wants a value for it ,which would probably not be his answer as he's passing strings by default.
The point is to force the strings to numeric, which '+' won't do. My suggestion accomplishes that easily.

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