convert pixels to other units of measurement back and forth, according to device DPI

unitConvert.js

/**
 * Convert pixels to other units of measurement, according to device DPI
 * 
 * @author   Pedro Sanção <dev at sancao dot co>
 * @license  MIT
 */
var unitConvert = (function(){
    var precision = 0
    , _setPrecision = function(p) {
        precision = p;
    }
    , _getElement = function() {
        var el = document.createElement('div');
        el.style.width = 0;
        el.style.visibility = 'hidden';
        document.body.appendChild(el);
        return el;
    }
    , _fixFloat = function(n) {
        return Number((n).toFixed(precision));
    }
    ;
    return {
        /**
         * approach 1 - increment until find the size
         * more precision require a lot of iterations
         * is faster with few pixels and low precision (0 or 1)
         */
        px2unit_incremental: function(unit, px, precision) {
            var el = _getElement()
            , pow = Math.pow(10, precision)
            , increment = 1 / pow
            , width = 0, lastWidth
            , iterations = 0
            ;
            _setPrecision(precision);
            do {
                iterations++;
                width = _fixFloat(width + increment);
                el.style.width = width + unit;
            } while (el.offsetWidth === 0);
            width = Math.floor(width * pow * px / el.offsetWidth) / pow;
            while (true) {
                iterations++;
                lastWidth = el.style.width;
                el.style.width = width + unit;
                if (el.offsetWidth > px) {
                    el.style.width = lastWidth;
                    break;
                }
                width = _fixFloat(width + increment);
            }
            width = el.style.width;
            document.body.removeChild(el);
            console.log(iterations + ' iterations');
            return width;
        },
        /**
         * approach 2 - use binary search
         * faster when higher precisions are required
         */
        px2unit: function(unit, px, precision) {
            var el = _getElement()
            , pow = Math.pow(10, precision)
            , increment = 1 / pow
            , width = 0, lastWidth, min, max, avg
            , iterations = 0
            ;
            _setPrecision(precision);
            while (el.offsetWidth <= px) {
                iterations++;
                lastWidth = width;
                width = width ? width * 2 : increment;
                el.style.width = width + unit;
            }
            min = lastWidth;
            max = width;
            while (_fixFloat(max - min) !== increment) {
                iterations++;
				avg = Math.round((max + min) / 2 * pow * 10) / pow / 10;
				width = _fixFloat(Math.floor(avg * pow) / pow);
                el.style.width = width + unit;
                if (el.offsetWidth > px) {
                    max = width;
                } else {
                    min = width;
                }
            };
            document.body.removeChild(el);
            console.log(iterations + ' iterations');
            return min + unit;
        },
        unit2px: function(unit) {
            var el = _getElement(), width;
            el.style.width = unit;
            width = el.offsetWidth;
            document.body.removeChild(el);
            return width;
        }
    };
})();