JavaScript numbers to Words

Question

I\'m trying to convert numbers into english words, for example 1234 would become: \"one thousand two hundred thirty four\".

My Tact

Answer 1

Here's a solution that will handle any integer value that fit's in a string. I've defined number scales up to "decillion", so this solution should be accurate up to 999 decillion. After which you get things like "one thousand decillion" and so on.

JavaScript numbers start to fail around "999999999999999" so the convert function works with strings of numbers only.

Examples:

convert("365");
//=> "three hundred sixty-five"

convert("10000000000000000000000000000230001010109");
//=> "ten thousand decillion two hundred thirty billion one million ten thousand one hundred nine"

Code:

var lt20 = ["", "one", "two", "three", "four", "five", "six", "seven","eight", "nine", "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen" ],
    tens = ["", "ten", "twenty", "thirty", "fourty", "fifty", "sixty", "seventy", "eightty", "ninety" ],
    scales = ["", "thousand", "million", "billion", "trillion", "quadrillion", "quintillion", "sextillion", "septillion", "octillion", "nonillion", "decillion" ],
    max = scales.length * 3;

function convert(val) {
    var len;

    // special cases
    if (val[0] === "-") { return "negative " + convert(val.slice(1)); }
    if (val === "0") { return "zero"; }

    val = trim_zeros(val);
    len = val.length;

    // general cases
    if (len < max) { return convert_lt_max(val); }
    if (len >= max) { return convert_max(val); }
}

function convert_max(val) {
    return split_rl(val, max)
        .map(function (val, i, arr) {
            if (i < arr.length - 1) {
                return convert_lt_max(val) + " " + scales.slice(-1);
            }
            return convert_lt_max(val);
        })
        .join(" ");
}       

function convert_lt_max(val) {
    var l = val.length;
    if (l < 4) {
        return convert_lt1000(val).trim();
    } else {
        return split_rl(val, 3)
            .map(convert_lt1000)
            .reverse()
            .map(with_scale)
            .reverse()
            .join(" ")
            .trim();
    }
}

function convert_lt1000(val) {
    var rem, l;

    val = trim_zeros(val);
    l = val.length;

    if (l === 0) { return ""; }
    if (l < 3) { return convert_lt100(val); }
    if (l === 3) { //less than 1000
        rem = val.slice(1);
        if (rem) {
            return lt20[val[0]] + " hundred " + convert_lt1000(rem);
        } else {
            return lt20[val[0]] + " hundred";
        }
    }
}

function convert_lt100(val) {
    if (is_lt20(val)) { // less than 20
        return lt20[val];
    } else if (val[1] === "0") {
        return tens[val[0]];
    } else {
        return tens[val[0]] + "-" +  lt20[val[1]];
    }
}


function split_rl(str, n) {
    // takes a string 'str' and an integer 'n'. Splits 'str' into
    // groups of 'n' chars and returns the result as an array. Works
    // from right to left.
    if (str) {
        return Array.prototype.concat
            .apply(split_rl(str.slice(0, (-n)), n), [str.slice(-n)]);
    } else {
        return [];
    }
}

function with_scale(str, i) {
    var scale;
    if (str && i > (-1)) {
        scale = scales[i];
        if (scale !== undefined) {
            return str.trim() + " " + scale;
        } else {
            return convert(str.trim());
        }
    } else {
        return "";
    }
}

function trim_zeros(val) {
    return val.replace(/^0*/, "");
}

function is_lt20(val) {
    return parseInt(val, 10) < 20;
}