woodLength Javascript Kata

woodLength.js

// https://www.codewars.com/kata/how-much-wood/train/javascript
//
// Written for node v8.1.3
//
// nvm install v8.1.3
// nvm use v8.1.3
// node woodLength.js
//

function woodLength(dimensions) {
    function measurement(str) {
        // https://regex101.com/r/Z8aHuk/1
        const re = /^(?:(\d+)(['"]))? ?(?:(\d+)? ?(?:(\d+)\/(\d+))?(['"]))$/;
        const m = str.match(re);
        if (!m) throw str;
        const value = defaultValue => v => parseInt(v) || defaultValue;
        const units = {"'": 12, '"': 1};
        const unit = v => units[v] || 1;
        const defaults = [value(0), unit, value(0), value(0), value(1), unit];
        const values = m.slice(1, 1 + defaults.length);
        const [whole, wunit, fwhole, num, denom, funit] = values.map((v, i) => defaults[i](v));
        return whole * wunit + (fwhole + (num / denom)) * funit;
    }

    function toFractionalInch(n) {
        let b = 1;
        while (!Number.isInteger(n)) {
            b *= 2;
            n *= 2;
        }
        return [n, b];
    }

    let height, length, width;
    try {
        [height, length, width] = dimensions.map(x => measurement(x));
    } catch(e) {
        console.log('bad input: ' + e);
        return 'bad input: ' + e;
    }
    const need = 2 * (height + length + 4 * width);
    const feet = Math.floor(need / 12);
    let inches = need - feet * 12;
    const fraction = toFractionalInch(inches - Math.floor(inches));
    inches = Math.floor(inches);

    let s = [];
    if (feet) s.push(`${feet}'`);
    if (inches) s.push(inches);
    if (fraction[0]) s.push(fraction.join('/'));

    return s.join(' ') + ((inches || fraction[0]) ? '"' : '');
}

const tests = [
    [["1\'","1\'","1/2\""], "4\' 4\""],
    [["2\'","1\' 5\"","1/16\""], "6\' 10 1/2\""],
    [["2\'","1\' 5\"","1\""], "7\' 6\""],
    [["4\'","2\' 6\"","5/32\""], "13\' 1 1/4\""],
    [["7\"","9\"","2\""], "4\'"],
    [["a7\"","9\"","2\""], "4\'"],
];

tests.forEach(([input, output]) =>
              console.log("woodLength([" + input.join(', ') + "]) == " + output +
                          "  =>  " + (woodLength(input) == output))
             );