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I have the variable y, which is a subtotal. Its value is different depending on what happens with the html, but throughout the script I declared it like this:

var y = 21.78;

etc. Why is it that on my last equation where I add up the total, it treats them as strings when I want to add the values?

var tax = (0.055*y).toFixed(2);
var totalprice = y+tax;
/* totalprice holds "21.781.20" instead of 22.98 */
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5
  • @Radu no, just a series of if else statements. y is always equal to a number like that, no other variables are involved in declaring it. Commented Apr 9, 2012 at 21:23
  • 3
    For a question to be answerable, the problem must be reproducible. Please include minimal sample code: complete, concise and representative. Read Writing the Perfect Queston for more guidelines. Commented Apr 9, 2012 at 21:23
  • @outis - ooh I like that answer. I'm gonna have to save that somewhere so I can re-use it. Commented Apr 9, 2012 at 21:23
  • Actually, it looks like the sample code is complete. It' so rare that three lines is enough, I leapt to the conclusion it wasn't. Commented Apr 9, 2012 at 21:26
  • He could have done it with one line using commas. Commented Apr 9, 2012 at 22:18

5 Answers 5

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According to:

https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Number/toFixed

toFixed() returns:

A string representation of number that does not use exponential notation and has exactly digits digits after the decimal place.

thus, y+tax is cast to a string since one of the operands is a string.

In my opinion, this would make sense as Javascript's intrinsic numeric types do not have the ability to store a specific number of decimal place digits, so a string would be the most appropriate data structure to store this with.

I would advise you do all your addition before calling toFixed(), since the method is most suitable for formatting display output.

var taxRate = 0.055;
var subtotal = 21.78;

var tax = (taxRate * subtotal).toFixed(2),
totalprice = ((1+taxRate) * subtotal).toFixed(2);
document.write(totalprice);

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Comments

3

The .toFixed() method returns a string. Try applying that method as the last step after all other calculations.

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3

Here's a simple fix. Put '+' in front of the tax variable to convert it to a number.

var y = 21.78;
var tax = (0.055*y).toFixed(2);
var totalprice = y+ (+tax);
totalprice === 22.98;

If you don't want any rounding errors when you use toFixed, then include this re-implementation of it in your script. http://bateru.com/news/2012/03/reimplementation-of-number-prototype-tofixed/

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1

In my experience, if there's any chance available, Javascript will see the "+" sign as concatenate rather than addition. It's driven me nuts on more than one occasion. I will generally do this rather than chance concatenation:

var totalprice = parseInt(y)+parseInt(tax);
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1 Comment

typeof is your friend. So is an hour or two of googling how JS's dynamic type casting/conversion works. Much easier than hitting everything with the parse mallet which would have caused you problems in this case. You'll want parseFloat for numbers with decimals. parseInt(0.55) returns 0.
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When letter replaces value, multiply with 1 when you're in need of +. 

var totalprice = (y*1) + tax .

Other operands work fine, it's just the + operand that needs special treatment when variable replace value.

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1 Comment

Did you test this? It doesn't work. y is already a number and multiplying it by 1 won't do anything. The problem is that tax is a string. Also, what's the period doing at the end of the line?

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