systemjs/lib/extension-depCache.js

System loader extension for flexible AMD & CommonJS support

/*
 * Dependency Tree Cache
 * 
 * Allows a build to pre-populate a dependency trace tree on the loader of 
 * the expected dependency tree, to be loaded upfront when requesting the
 * module, avoinding the n round trips latency of module loading, where 
 * n is the dependency tree depth.
 *
 * eg:
 * System.depCache = {
 *  'app': ['normalized', 'deps'],
 *  'normalized': ['another'],
 *  'deps': ['tree']
 * };
 * 
 * System.import('app') 
 * // simultaneously starts loading all of:
 * // 'normalized', 'deps', 'another', 'tree'
 * // before "app" source is even loaded
 */

function depCache(loader) {
  loader.depCache = loader.depCache || {};

  loaderLocate = loader.locate;
  loader.locate = function(load) {
    var loader = this;

    if (!loader.depCache)
      loader.depCache = {};

    // load direct deps, in turn will pick up their trace trees
    var deps = loader.depCache[load.name];
    if (deps)
      for (var i = 0; i < deps.length; i++)
        loader.load(deps[i]);

    return loaderLocate.call(loader, load);
  }
}