An Interest In:
Web News this Week
- March 19, 2024
- March 18, 2024
- March 17, 2024
- March 16, 2024
- March 15, 2024
- March 14, 2024
- March 13, 2024
JavaScript question Day 4
Which one is true ?
const bird = { size: 'small',};const mouse = { name: 'Mickey', small: true,};
- A:
mouse.bird.size
is not valid - B:
mouse[bird.size]
is not valid - C:
mouse[bird["size"]]
is not valid - D: All of them are valid
Answer: A
In JavaScript, all object keys are strings (unless it's a Symbol). Even though we might not type them as strings, they are always converted into strings under the hood.
JavaScript interprets (or unboxes) statements. When we use bracket notation, it sees the first opening bracket [
and keeps going until it finds the closing bracket ]
. Only then, it will evaluate the statement.
mouse[bird.size]
: First it evaluates bird.size
, which is "small"
. mouse["small"]
returns true
However, with dot notation, this doesn't happen. mouse
does not have a key called bird
, which means that mouse.bird
is undefined
. Then, we ask for the size
using dot notation: mouse.bird.size
. Since mouse.bird
is undefined
, we're actually asking undefined.size
. This isn't valid, and will throw an error similar to Cannot read property "size" of undefined
.
Original Link: https://dev.to/soorajs98/javascript-question-day-4-el6
Dev To
An online community for sharing and discovering great ideas, having debates, and making friendsMore About this Source Visit Dev To