How can I work around the immutability of a string in Javascript?

Question

Since strings are immutable in Javascript, how can I use user's input for conversions?

I was trying to use a function that changes an hexadecimal color code's digits into decimal numbers, but got stuck with the immutable property of strings. I tried copying each character to an array using "for", but the new array was still unoperable. Here is the code sample for what I was trying to do:

var user_input = prompt("Please enter an hexadecimal color code:","e.g. A876FF");

        var hexa_to_dec = function(hexa_code)/*changes each digit from hexadecimal to decimal*/

       {
        for(i = 0; i < hexa_code.length; i++)

            {
            if (isNaN(hexa_code[i]))

                {
                switch(hexa_code[i])

                    {
                    case "A" : hexa_code[i] = 10; break;
                    case "B" : hexa_code[i] = 11; break;
                    case "C" : hexa_code[i] = 12; break;
                    case "D" : hexa_code[i] = 13; break;
                    case "E" : hexa_code[i] = 14; break;
                    case "F" : hexa_code[i] = 15; break;
                    }

                }

            }

        document.write(hexa_code);
        }

    hexa_to_dec(user_input);

adeneo · Accepted Answer · 2015-01-28 13:20:29Z

2

Seems like there should be an easier way to do that, for instance just writing the result of the string manipulation back to the same variable

var user_input = prompt("Please enter an hexadecimal color code:","e.g. A876FF");

user_input = user_input.replace(/[ABCDEF]/g, function(x) {
    return {A:10,B:11,C:12,D:13,E:14,F:15}[x];
});

document.body.innerHTML = user_input;

FIDDLE

answered Jan 28, 2015 at 13:20

adeneo

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2 Comments

Amberlamps Over a year ago

Replacing the return statement with this return x.toUpperCase().charCodeAt(0) - 55; will add more obscurity.

adeneo Over a year ago

@Amberlamps - I like that, and think it's pretty clever.

collardeau · Accepted Answer · 2015-01-28 13:48:17Z

Because hexa_code is a string and is immutable, you cannot write back to it, like when you try hexa_code[i] = 10 in your switch statement.

Make a new variable to store your result.

Here, see the working code below (also at http://jsfiddle.net/legolandbridge/pn1t4jz1/)

var user_input = prompt("Please enter an hexadecimal color 

    code:","e.g. A876FF");

    var hexa_to_dec = function(hexa_code) {

            var output = "";

            for(var i = 0, limit=hexa_code.length; i < limit; i++) {

                    switch(hexa_code[i]){ 
                        case "A" : output += 10; break;
                        case "B" : output += 11; break;
                        case "C" : output += 12; break;
                        case "D" : output += 13; break;
                        case "E" : output += 14; break;
                        case "F" : output += 15; break;
                        default: output += hexa_code[i];
                        }

                    }

            console.log(output);
            };

    hexa_to_dec(user_input);

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