SystemJS translate hook that caches transpilation results of sources that haven't changed in IndexedDB storage.

plugin-translate-cache.js

/**
 * SystemJS translate hook that caches transpilation results of sources that haven't changed in IndexedDB storage.
 * In Chrome dev tools the cache is easily managed under Resources > IndexedDB > jspm
 * There's a global dependency on Dexie.js (ex: //npmcdn.com/[email protected]/dist/dexie.min.js)
 * Adapted from https://gist.github.com/ineentho/3ccaaec164e418f685d7
 */
;(function(){
    var db = new Dexie("jspm");
    db.version(1).stores({ files: "&url,format,hash,contents" });
    db.open();

    var log = console.log.bind(console);

    System.originalTranslate = System.translate;
    System.translate = function (load) {
        if (!load.metadata.deps) {
            load.metadata.deps = []; // avoid https://github.com/systemjs/systemjs/pull/1158
        }

        function hash(str) {
            // Source: http://stackoverflow.com/a/7616484/502126
            var hash = 0, i, chr, len
            if (str.length === 0) return hash
            for (i = 0, len = str.length; i < len; i++) {
                chr   = str.charCodeAt(i)
                hash  = ((hash << 5) - hash) + chr
                hash |= 0
            }
            return hash.toString()
        }

        var file = {url:load.address, hash:hash(load.source)};
        var loader = this;

        return db.files.where('url').equals(file.url).first().then(function(cached) {
            if (!cached || cached.hash != file.hash) {
                return System.originalTranslate.apply(loader, [load]).then(function(translated) {
                    file.format = load.metadata.format;
                    file.contents = translated;
                    
					return (cached ? db.files.delete(file.url) : Promise.resolve())
						.then(db.files.add(file))
						.then(function() {
							return translated;
						}).catch(log);
                });
            } else {
                load.metadata.format = cached.format || undefined;
                return cached.contents;
            }
        }).catch(log);
    }
})();