requireJS optional dependency

Question

I'm adding AMD support to a javascript library I develop.

This library may use jquery but it will still work if jquery isn't loaded.

When defining the module dependency there's a way to set a dependency as 'optional' so that if that library is missing the module will still work?

Answer 1

I've had exactly the same problem recently, and here's how I fixed it. I defined a RequireJS plugin called optional which ignores modules that fail to load by explicitly defining them as an empty object (but I suppose you could also define it as null or anything else if you wanted).

Here is the code (tested with RequireJS 2.1.15):

define("optional", [], {     load : function (moduleName, parentRequire, onload, config){          var onLoadSuccess = function(moduleInstance){             // Module successfully loaded, call the onload callback so that             // requirejs can work its internal magic.             onload(moduleInstance);         }          var onLoadFailure = function(err){             // optional module failed to load.             var failedId = err.requireModules && err.requireModules[0];             console.warn("Could not load optional module: " + failedId);              // Undefine the module to cleanup internal stuff in requireJS             requirejs.undef(failedId);              // Now define the module instance as a simple empty object             // (NOTE: you can return any other value you want here)             define(failedId, [], function(){return {};});              // Now require the module make sure that requireJS thinks              // that is it loaded. Since we've just defined it, requirejs              // will not attempt to download any more script files and             // will just call the onLoadSuccess handler immediately             parentRequire([failedId], onLoadSuccess);         }          parentRequire([moduleName], onLoadSuccess, onLoadFailure);     } }); 

You can then require a module optionally using simply

require(['optional!jquery'], function(jquery){...}); 

knowing that if the jquery module could not be loaded, the parameter passed to your callback function will be an empty object.

Answer 2

You cannot really set it optional, but you can catch the error and unload the module using undef:

require(['jquery'], function ($) {     //Do something with $ here }, function (err) {     //The errback, error callback     //The error has a list of modules that failed     var failedId = err.requireModules && err.requireModules[0];     if (failedId === 'jquery') {         //undef is function only on the global requirejs object.         //Use it to clear internal knowledge of jQuery. Any modules         //that were dependent on jQuery and in the middle of loading         //will not be loaded yet, they will wait until a valid jQuery         //does load.         requirejs.undef(failedId);         ...      } }); 

Full example here.