Test for existence of nested JavaScript object key

If I have a reference to an object: var test = {}; that will potentially (but not immediately) have nested objects, something like: {level1: {level2: {level3: "level3"}}}; What is the best way to check for the existence of property in deeply nested objects? alert(test.level1); yields undefined, but alert(test.level1.level2.level3); fails. I’m currently doing something like this: if(test.level1 &&