View Full Version : 1 + 1 will output 11 and not 2...

Dennis_Gull

07-04-2007, 12:21 AM

Hello, got a problem with addition, I have a function that will need a number. Like:

my_function(numb)

and now I want to get the next number (numb + 1) but It will output as 11 instead of 1 + 1 = 2..

I tried to use this:

var next = numb + 1..

and this:

var next = 0;

next = numb + 1;

and this:

var one = 1;

var next numb + one;

but it will give me the same result all the time, the previous (-1) works great but not the +1..

thetestingsite

07-04-2007, 12:40 AM

Try numb++, usually that works.

Dennis_Gull

07-04-2007, 01:05 AM

thanks it worked.

The + operator in Javascript is overloaded: it performs two quite distinct functions. It performs arithmetical addition on numbers, but concatenation on strings. The latter always takes precedence over the first, so if a string is involved on either side of the operator, concatenation will occur. That is to say:

1 + 1 == 2;

1 + "1" == "11";

"1" + 1 == "11";If you're not sure whether you're dealing with a number or a string, be safe and convert it. There are several methods of doing this:

new Number(n);

parseFloat(n, 10);

parseInt(n, 10);

n - 0;

-n;

+n;

n * 1;

djr33

07-04-2007, 02:36 AM

Isn't the easiest way, then to do

a + 1*b; ?

(Assuming you know that a is a constant, or that a is declared literally as an integer, say 3 + 1*b; )

Or, you could just subtract it's opposite:

a-(-b);

That's probably the easiest, in fact. This would, since it's a mathematical operation without a string-alternative, convert both a and b, I'd assume, so it's a very efficient way to do all of this at once.

Trinithis

07-04-2007, 05:34 AM

Are the (a+b*1) or (a- -b) shorthands executed faster than the parse functions?

djr33

07-04-2007, 06:05 AM

My guess would be that any simple math function would be faster than any more complex function.

Yes, +"3" performed an average of 0.0053ms faster than parseInt("3", 10) over 100,000 iterations in SpiderMonkey.

Digger3000

07-04-2007, 11:50 AM

I would just do this:

var next=numb-0+1;

Personally, I prefer the form:

var next = +numb + 1;However, be aware that parse(Int|Float) don't do quite the same things as the simple operator trickery; they will ignore trailing characters, for a start. +"3j" is NaN, but parseInt("3j") is 3.

mwinter

07-04-2007, 05:12 PM

If you're not sure whether you're dealing with a number or a string, be safe and convert it. There are several methods of doing this:

new Number(n);

No! That evaluates to a Number object, not a number. Whilst it should work, it will involve further conversion (through use of the valueOf method). Instead, call the constructor function as a function:

Number(n)

-n;

Just to point out the obvious: this will evaluate to a number with reversed sign.

Isn't the easiest way, then to do

a + 1*b; ?

There isn't really any objective answer to that, though for compactness I would use unary plus (+) and for readability, the Number constructor function:

a + (+b)

a + Number(b)

The parentheses emphasis the meaning, as well as help prevent an accident like confusing "+ +b" for "++b".

Yes, +"3" performed an average of 0.0053ms faster than parseInt("3", 10) over 100,000 iterations in SpiderMonkey.

Unary plus should be the fastest of all techniques.

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