less.js/lib/less-browser/cache.js

// Cache system is a bit outdated and could do with work

module.exports = function(window, options, logger) {
    var cache = null;
    if (options.env !== 'development') {
        try {
            cache = (typeof window.localStorage === 'undefined') ? null : window.localStorage;
        } catch (_) {}
    }
    return {
        setCSS: function(path, lastModified, modifyVars, styles) {
            if (cache) {
                logger.info('saving ' + path + ' to cache.');
                try {
                    cache.setItem(path, styles);
                    cache.setItem(path + ':timestamp', lastModified);
                    if (modifyVars) {
                        cache.setItem(path + ':vars', JSON.stringify(modifyVars));
                    }
                } catch (e) {
                    // TODO - could do with adding more robust error handling
                    logger.error('failed to save "' + path + '" to local storage for caching.');
                }
            }
        },
        getCSS: function(path, webInfo, modifyVars) {
            var css       = cache && cache.getItem(path),
                timestamp = cache && cache.getItem(path + ':timestamp'),
                vars      = cache && cache.getItem(path + ':vars');

            modifyVars = modifyVars || {};
            vars = vars || "{}"; // if not set, treat as the JSON representation of an empty object

            if (timestamp && webInfo.lastModified &&
                (new Date(webInfo.lastModified).valueOf() ===
                    new Date(timestamp).valueOf()) &&
                JSON.stringify(modifyVars) === vars) {
                // Use local copy
                return css;
            }
        }
    };
};