Programming > JavaScript and DHTML > Chapter 2. Numbers and Dates > 2.6 Converting Between Decimal and Hexadecimal Numbers

NN 2, IE 3

2.6.1 Problem

You want to change a decimal number to its hexadecimal equivalent, and vice versa.

2.6.2 Solution

While the core JavaScript language provides facilities for going from hexadecimal to decimal, you need a custom function to go the other way.

To get a hexadecimal number as a string into its decimal equivalent, use the parseInt( ) method and specify the second parameter as 16:

var decimalVal = parseInt(myHexNumberValue, 16);

For myHexNumberValue, you can use either the hexadecimal characters for the number, or the format required for hexadecimal arithmetic in JavaScript: the hexadecimal characters preceded by 0x or 0X (a zero followed by an X). Here are some examples with string literals in the two formats:

var decimalVal = parseInt("1f", 16);
var decimalVal = parseInt("0x1f", 16);

To convert a decimal number (between 0 and 255) to a hexadecimal string equivalent, use the following function:

function dec2Hex(dec) {
    dec = parseInt(dec, 10);
    if (!isNaN(dec)) {
        hexChars = "0123456789ABCDEF";
        if (dec > 255) {
            return "Out of Range";
        }
        var i = dec % 16;
        var j = (dec - i) / 16;
        result = "0x";
        result += hexChars.charAt(j) + hexChars.charAt(i);
        return result;
    } else {
        return NaN;
    }
}

Because JavaScript automatically converts hexadecimal numbers to their decimal equivalents for arithmetic operations, the hexadecimal conversion is needed only for display of a hexadecimal result.

2.6.3 Discussion

Hexadecimal arithmetic isn't used much in JavaScript, but the language provides rudimentary support for base 16 numbers. As long as you signify a hexadecimal number value with the leading

0x, you can perform regular arithmetic on that value to your heart's content. But be aware that the results of those operations are returned in base 10, which allows the odd possibility of using hexadecimal and decimal values in the same expression:

var result = 0xff - 200;

Hexadecimal digits a through f may be expressed in your choice of upper- or lowercase letters.

The parseInt( ) method is frequently a handy tool for getting values in other bases into decimal. For example, you obtain a decimal equivalent of a binary number string by specifying base 2 as the second argument of the method:

var decimalVal = parseInt("11010011", 2);

2.6.4 See Also

Recipe 2.1 for converting between number and string value types.