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JavaScript Objects, Destructuring and Immutability, what does console.log(firstItem) print after const { list: [firstItem] } = { list: ['a', 'b'] }?
Block 5, Objects, Destructuring and Immutability, question 19 of the JavaScript sample
const { list: [firstItem] } = { list: ['a', 'b'] };
console.log(firstItem);What does this print?
Show the answer and why each option is right or wrong
Answer, A. a
- A. a
- Correct. The nested array pattern takes the first element of list, which is the string a.
- B. ["a","b"]
- Assumes list, once renamed inside the pattern, ends up holding the whole array instead of just its first element.
- C. undefined
- Assumes mixing object and array destructuring in a single pattern is not supported.
- D. b
- Assumes an array pattern nested inside an object pattern takes the last element rather than the first.
Object and array destructuring patterns can be nested inside each other freely. An array pattern used as the value of an object property destructures the array found at that property using ordinary positional rules, starting from index 0.
The answer above is what the Node interpreter printed when the snippet was run, not what someone expected it to do.
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