Strange string concat

edislasm · September 3rd, 2005, 01:47 PM

Hi, this seems to be stupid but i find no explanation. I have this lines for testing the problem:

var cantidad;
cantidad = 0;
cantidad = cantidad + parseInt(document.forms[0].Cantidad.value);
cantidad = cantidad + parseInt(document.forms[0].Cantidad2.value);

the form can accept empty values and it seems that parseInt('') = NaN so, as I would do in VBscript or in Java, could fix the problem like this:

var cantidad;
cantidad = 0;
cantidad = cantidad + parseInt('0' + document.forms[0].Cantidad.value);
cantidad = cantidad + parseInt('0' + document.forms[0].Cantidad2.value);
alert(cantidad);

but it seems that a zero on the left does real diference!. For example, for a value in Cantidad2 of '1', I can put any value from '0' to '7' and even empty string. But after number '8' I don't really get the sum of Cantidad1 + 1. This is the arithmetics that is doing for example:

'' + 1 = 1
'4' + '1' = 5
'8' + '1' = 1
'200' + '1' = 129

Strange huh?... and how to fix this??

philip_cole · September 5th, 2005, 01:03 PM

hmmm interesting. I played around, and it looks like it treats the value as octal (base 8). This means:
0-7 is same,
8 and 9 get ignored (are parsed as zero),
200 is 8*8*2 +0+0 = 128.

I would get round this by checking if the values are empty first:

var cantidad;
cantidad = 0;
if(document.forms[0].Cantidad.value.length > 0)
cantidad = cantidad + parseInt(document.forms[0].Cantidad.value);
if(document.forms[0].Cantidad2.value.length > 0)
cantidad = cantidad + parseInt(document.forms[0].Cantidad2.value);
alert(cantidad);

.. or ask them to enter the numbers in octal :)

Philip Cole

joefawcett · September 6th, 2005, 02:17 AM

As Philip has pointed out parseInt treats sequences starting with 0 as octal. Either specify the base you are converting to:

Code:

parseInt(Cantidad, 10);

or don't use it all, I'm not sure why parseInt is always used in examples, use

Code:

 Math.floor(Cantidad);

--

Joe (Microsoft MVP - XML)