How can I add a number to a variable to which I assigned a number in Javascript?

Question

I have the following:

var offset;
offset = localStorage.getItem('test.MenuList.Offset.' + examID + "." + level) || 0;
offset += 100;

When I use the debugger this offset now has 0100. I want it to add like a number not a string. How can I do this?

Please note I changed the question slightly because I realized I was getting the value from local storage. I assume this returns a string. But I am still not sure how to solve this.

David - Sorry. I updated the question. I think this is my problem. I get the value from localStorage. — user1679941
– user1679941, Commented Oct 7, 2012 at 13:43
Sorry David. Please see my change to the question. If I do: offset = "0"; then it gives "0100" :-( — user1679941
– user1679941, Commented Oct 7, 2012 at 13:45
Anything inside quotes is a string, and adding "0" and 100 would be the same as adding "B" and 100, which would give you "B100" etc. — adeneo
– adeneo, Commented Oct 7, 2012 at 13:46

I Hate Lazy · Accepted Answer · 2012-10-07 13:46:10Z

2

~~The code you gave won't do that. I assume~~ your value in your actual code is a numeric string. ~~If so,~~ the + will behave as a string concatenation operator, so you must convert the value to a number before using +.

You can do that with parseFloat().

var offset = localStorage.getItem('test.MenuList.Offset.' + examID + "." + level);

offset = parseFloat(offset) || 0;

Or in most cases, you can simply use the unary version of + to do the conversion.

offset = +offset || 0;

edited Oct 7, 2012 at 13:46

answered Oct 7, 2012 at 13:40

I Hate Lazy

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