Salesforce JavaScript Developer Practice Exam

Which statement about the bird and mouse objects is correct?

1. mouse.bird.size is not valid

2. mouse[bird.size] is not valid

3. mouse[bird["size"]] is not valid

4. All of them are valid

The correct answer is: mouse.bird.size is not valid

The statement that mouse.bird.size is not valid is correct because it suggests an attempt to access the property "bird" of the object "mouse." For this to be valid, the "mouse" object must have a property named "bird." If this property does not exist, trying to access it will lead to an undefined value, and consequently accessing "size" on an undefined object would be invalid in JavaScript. In contrast, accessing properties using bracket notation, as in the other statements, is generally more flexible, allowing for the use of dynamic keys. However, these statements depend on the actual structure of the objects. If "mouse" does not have a property that can be validly accessed, then the statements that involve bracket notation might also yield invalid results. Thus, understanding the context and structure of the objects involved is crucial. Given that the question does not provide specific definitions for "mouse" and "bird" objects, it reinforces why the claim about mouse.bird.size can be considered correct in a generalized sense.