library function for safe property reference on javascript objects

Question

Consider the following code:

function foo(handlers) {
  callSomeFunction(handlers.onSuccess, handlers.onFailure);
}

The caller may do:

foo({onSuccess: doSomething, onFailure: doSomethingElse });

or simply just

foo()

if s/he has nothing special to do.

The issue with the above code is that if 'handlers' are undefined, like in the simple foo() call above, then a run-time exception will be thrown during the execution of callSomeFunction(handlers.onSuccess, handlers.onFailure).

For handling such situations one may re-write the foo function as:

function foo(handlers) {
  var _handlers = handlers || {};
  callSomeFunction(_handlers.onSuccess, _handlers.onFailure);
}

or more structured

function safe(o) {
  return o === Object(o) ? o : {};
}

function foo(handlers) {
  callSomeFunction(safe(handlers).onSuccess, safe(handlers).onFailure);
}

I tried to find something like the safe() function in libraries such as sugarjs and underscore, but found nothing. Did I miss something? Is there any other utility library that has a similar function?

Just trying not to reinvent the wheel... ;)

BR, Adrian.

P.S. I didn't test the code above, so it may have errors.

Answer 1

There is something pretty similar in jQuery, often used when dealing with plugin development wich is jQuery.extend:

function foo(options){
    var defaults = {onSuccess: someFunction, onFailure: someOtherStuff}
    var options = $.extend({}, defaults, options); 
}

In this case it make sense, because user can provide an arbitrary subset of options, and the function with add the defaults for those not provided in the function call.