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Sean Gibson
38,363 Pointsdot vs. no dot in constant declaration
I'm a bit confused about this part of the code:
const text = cards[id][side];
const hint = cards[id].hint;
Why does hint use dot notation ( [id].hint) while text does not? Are question/answer and hint not all properties of a specific json object (cards[1].property)? When I try changing to text = cards[id].[side] it crashes. Is it perhaps because side is not specifically defined as a property we should treat this part as a 2-dimension array? I'm merely speculating at this point so could someone please help out?
2 Answers
Jason Larson
8,353 PointsI have not watched the video, but your question is about object properties. There are 2 ways to specify the properties of an object. The one that is more common is the dot notation, as in
const hint = cards[id].hint;
You can also refer to an object property by using bracket notation, where you specify the property name inside the brackets, like
const text = cards[id][side];
You had 2 problems when you changed it to text = cards[id].[side]. First, you combined dot notation with the bracket notation. If you're going to do it like that, it should be const text = cards[id].side;. Unfortunately, you can't use dot notation like that if the property name is stored in a variable. I believe dot notation may just be syntactic sugar for the bracket notation and is expecting the value after the dot to be a property name, and does not convert it from a string variable.
As for your question about treating it like a 2d array, that would only be applicable if cards[id] is an array and side is a number. Since you're other example apparently works, I'm guessing cards[id] is an object and not an array. I'm also assuming side in this code represents a string.
Sean Gibson
38,363 PointsThanks, Jason. Your answer was quite helpful in reminding me of bracket vs. dot notation. In the video, side is a variable that will (depending on the url query string) be either question or answer, which do happen to be properties of the JSON object cards[x]. However, if I change cards[id][side] to cards[id].side the program doesn't run properly. It doesn't crash, but it doesn't display properly. Is this perhaps because when using variables one MUST use bracket notation? That's the only thing I can come up with. Please tell me I'm at least on the right track ;-)
Jason Larson
8,353 PointsSean, you're absolutely right. I forgot about the requirement for using bracket notation when using a variable for the property name. I knew there were times when you had to use bracket notation, I just forgot what they were. I'll update my original answer so that anybody else with the same question won't have the same issue you did.