JavaScript Maps and Sets Quiz

To pass the quiz, you must correctly answer at least 18 of the 20 questions below. # --quizzes-- ## --quiz-- ### --question-- #### --text-- What is a Set in JavaScript? #### --distractors-- A data structure that allows duplicate values. --- A data structure that only stores strings and numbers. --- A collection that does not allow deletion of its elements. #### --answer-- A collection in which a value can only occur once. ### --question-- #### --text-- Which of the following methods is available in Maps but not in Sets? #### --distractors-- `has()` --- `clear()` --- `values()` #### --answer-- `set()` ### --question-- #### --text-- What method is used to add elements to a Set? #### --distractors-- `.push()` --- `.append()` --- `.insert()` #### --answer-- `.add()` ### --question-- #### --text-- How do you check if a Set contains a certain value? #### --distractors-- `.contains()` --- `.hasValue()` --- `.find()` #### --answer-- `.has()` ### --question-- #### --text-- Which of these is a great use case for Sets? #### --distractors-- Managing key-value pairs in a database. --- Creating ordered lists of items. --- Storing hierarchical data structures in the browser local storage. #### --answer-- Eliminating duplicates from an array. ### --question-- #### --text-- What is a WeakSet in JavaScript? #### --distractors-- A Set-like collection that only allows primitive data types. --- A Set-like collection that allows duplicate values. --- A Set-like collection that prevents values from being removed. #### --answer-- A Set-like collection that only stores objects. ### --question-- #### --text-- What is one difference between a Set and a WeakSet? #### --distractors-- A WeakSet can store any type of value, including numbers. --- A Set does not allow duplicate values, but a WeakSet does. --- A Set allows garbage collection, whereas a WeakSet does not. #### --answer-- A Set can hold any type of value, while a WeakSet only holds objects. ### --question-- #### --text-- What is a Map in JavaScript? #### --distractors-- A collection that only allows unique values. --- A collection that can only use strings as keys. --- A collection that does not allow deletion of its items. #### --answer-- A collection of key-value pairs of any type. ### --question-- #### --text-- What method is used to insert key-value pairs into a Map? #### --distractors-- `.append()` --- `.add()` --- `.insert()` #### --answer-- `.set()` ### --question-- #### --text-- What will the following code output? ```js const myMap = new Map(); myMap.set('a', 1); myMap.set('a', 2); console.log(myMap.get('a')); ``` #### --distractors-- `1` --- `undefined` --- `null` #### --answer-- `2` ### --question-- #### --text-- How does a Map differ from an Object in JavaScript? #### --distractors-- A Map only allows numbers as keys. --- Objects allow any type as keys, while Maps only allow strings. --- Maps do not support iteration, while Objects do. #### --answer-- Maps allow any type of key, but Objects only allow strings and symbols. ### --question-- #### --text-- How can you remove a key-value pair from a Map? #### --distractors-- `.remove()` --- `.deleteKey()` --- `.erase()` #### --answer-- `.delete()` ### --question-- #### --text-- What does the `size` property of a Map return? #### --distractors-- The number of indexes in the Map. --- The number of unique values in the Map. --- The total memory used by the Map. #### --answer-- The number of key-value pairs in the Map. ### --question-- #### --text-- What is a WeakMap in JavaScript? #### --distractors-- A Map-like collection that allows primitive values as keys. --- A Map-like collection that blocks the deletion of items. --- A Map-like collection that automatically sorts its keys. #### --answer-- A Map-like collection with weak references to the keys. ### --question-- #### --text-- What is one difference between a Map and a WeakMap? #### --distractors-- A Map allows only primitive types as keys, whereas a WeakMap only allows objects. --- A Map allows garbage collection, whereas a WeakMap does not. --- A WeakMap allows duplicate keys, whereas a Map does not. #### --answer-- A Map is iterable, whereas a WeakMap is not. ### --question-- #### --text-- Which of the following methods does NOT exist on a WeakMap? #### --distractors-- `.has()` --- `.set()` --- `.delete()` #### --answer-- `.size()` ### --question-- #### --text-- What will be the output of the following code? ```js const set = new Set([1, 2, 3]); set.delete(2); console.log(set.has(2)); ``` #### --distractors-- `true` --- `undefined` --- `2` #### --answer-- `false` ### --question-- #### --text-- How can you iterate over the values in a Set? #### --distractors-- By using the `.map()` method. --- By using the `.reduce()` method. --- By using the `.filter()` method. #### --answer-- By using the `.forEach()` method. ### --question-- #### --text-- Which two methods of Sets return a `SetIterator` that contains the values of a certain Set? #### --distractors-- `entries()` and `values()` --- `forEach()` and `values()` --- `has()` and `add()` #### --answer-- `keys()` and `values()` ### --question-- #### --text-- What will be the output of the following code? ```js const map = new Map([["a", 1], ["b", 2]]); map.clear(); console.log(map.size); ``` #### --distractors-- `2` --- `1` --- `undefined` #### --answer-- `0`