30 Aug 2012
This one cost me a CoderByte challenge today.
The challenge was, at a glance, simple enough: make a function that takes a binary number as input return the corresponding decimal value.
That’s easy in Javascript: just use parseInt and pass it the number and the base.
The problem was that some of the test cases started with 0: for instance, 011 (decimal 3).
To Javascript, that’s a base-8 number (octal), so the parseInt would return 9 (base 10) instead of 3.
I tried a couple of things (like casting it to string before calling parseInt or surrounding it with single quotes) before searching for help, which I found in CoderByte’s own forum.
There, another user had asked for help with exactly the same problem to which user 64kps answered with this:
return parseInt(num.toString(("" + num).match("[^01]") ? 8 : 10), 2);
As you can see, he also casts the number to string ("" + num) but next he checks if the resulting value starts with a zero or with an one (.match("^[01]")). If it starts with a zero, he then uses 8 as the base; otherwise, he uses 10 as the base. This base is then passed into the toString method and the resulting value is finally ready to be passed to parseInt. In more steps, this would be:
var base = ("" + num).match("[^01]") ? 8 : 10;
var valueToConvert = num.toString(base);
var result = parseInt(valueToConvert);
return result;
You can read the original forum thread here.