javascript: convert hexadecimal value into signed 8-bit integer

Question

I need a way of getting a signed 8-bit integer from a hexadecimal value using JavaScript. So far I have tried using parseInt(value, 8) but it seems to be deprecated and I get parseInt(0xbd, 8) = 0 (when it's supposed to give -67).

How can I do this?

I gave a solution for a similar problem here: http://stackoverflow.com/a/34679269/2102748, hope it helps. — milosmns, Jan 08 '16 at 14:23

score 11 · Accepted Answer · answered Aug 12 '15 at 23:19

I was just searching for a solution to this in javascript. The answer from splig does not seem correct, but it lead me to the solution.

I believe you should be subtracting 256 from num when (num > 127).

var num = parseInt('ff', 16);
if (num > 127) { num = num - 256 }
alert(num);

score 1 · Answer 2 · answered Aug 28 '14 at 10:37

The second parameter of parseInt is the radix, you need 16 as it's hex because you've told it it's hex the 0x is optional.

As you're wanting to do an 8 bit signed int you'll need convert it to signed manually - try something like

var num = parseInt('bd', 16);
if (num > 127) { num = 128 - num }
alert(num);

javascript: convert hexadecimal value into signed 8-bit integer

2 Answers2