code: function nodeModulesResolverFn(normalizedId) {
  		if (!nodeModulesAt) {
  			throw new Error('Before you can load external dependencies, you must specify where node_modules can be found by ' +
  				'setting the \'nodeModulesAt\' option when creating the context');
  		}
  
  		var extId = normalizedId.id;
  
  		var modulePath = path.join(nodeModulesAt, extId);
  		if (!externalDepExists[modulePath]) {
  			// yes I know the docs don't like this method.
  			// But it's a little better user experience than trying to require a file that isn't there.
  			if (fs.existsSync(modulePath)) {
  				externalDepExists[modulePath] = true; // cache it so we avoid the lookup next time
  
  			} else {
  				var msg = 'Could not find external dependency [' + extId + '] at path [' + modulePath + ']';
  				throw new Error(buildMissingDepMsg(msg, extId, allExternalIds()));
  			}
  
  		}
  
  		return require(modulePath);
  	}
docs: Requires modules from the node_modules directory