If a key includes one or more spaces, then you must use bracket notation. Otherwise, you are free to use either bracket or dot notation. In my experience, it’s far more common for programmers to not use spaces in their property names, so dot notation is what I see the most. Bracket notation is handy if you’ve gotten your data from a third party, like some web API or a database. In that case, you’re far more likely to see spaces in the object keys.