Javascript - Shorthand notation to safely check/access a property on a potential undefined object

Question

What's the shortest syntax to check if jsonObject is not undefined before accessing its errorMessage property?

var jsonObject = SomeMethodReturningAnObject();

if (jsonObject.errorMessage === undefined) // jsonObject can be undefined and this will throw an error
   /* success! */
else
   alert(jsonObject.errorMessage);

Answer 1

You can use the && operator, since it doesn't evaluate the right-hand side if the left-hand side is undefined:

if (jsonObject && jsonObject.errorMessage === undefined)