Synopsis:
new Map(): In JavaScript, new Map() is used to create a new Map object, which is a collection of key-value pairs where keys are unique and values can be repeated.
new Set(): In JavaScript, new Set() is the syntax used to create a new Set object, which is a collection of unique values with no duplicates. new Set() can be used to create an empty Set object by passing in an array or array-like object at creation time, and Set will automatically remove duplicate values.
new Map()
I. new Map() Basic Features
new Map() is the constructor used to create a new Map object.The Map object holds the key-value pairs and remembers the original insertion order of the keys. This means that you can iterate over the Map object and get the key-value pairs in the order in which the keys were inserted.
Map objects are different from normal objects (which use strings as keys) because a Map can use any type as a key (including functions, objects, or any raw value), not just strings or symbols.
II. Relevant methodology
1. set(key, value) : Adds a key-value pair to the Map object.
2. get(key) : Get the value corresponding to the specified key.
3. has(key) : Determines whether the specified key exists in the Map object.
4. delete(key) : Deletes the specified key and its corresponding value.
5. size : Returns the number of key-value pairs in the Map object.
6. clear() : Clear all key-value pairs in the Map object.
7. keys() : Returns an iterator of all the keys in the Map object.
8. values() : Returns an iterator containing all the values in the Map object.
9. entries() : Returns an iterator containing all key-value pairs in the Map object.
III. Basic use
// Create a new Map object let myMap = new Map(); // 1. Add key-value pairs ('name', 'Alice'); ('age', 25); // 2、Get the value (('name')); // Output: "Alice" // 3. Check if the key exists (('age')); // Output: true // 4. Delete key-value pairs myMap.delete('name'); (('name')); // Output: false // 5. Get the size of the Map (); // Output: 1 // 6. Empty Map (); (); // Output: 0 // 7. Iterate over the keys for (let key of ()) { (key); // Output: "age" } // 8, traversing the value for (let value of ()) { (value); // Output: 25 } // 9, traversing key-value pairs for (let [key, value] of ()) { (`Key: ${key}, Value: ${value}`); // Output: Key: age, Value: 25 }
new Set()
I. new Set() Basic Features
Uniqueness: In Set, each value appears only once, allowing for simple array de-duplication; even if two objects are identical, they will only be stored once in Set.
Unordered: The elements of a Set are in no particular order.
II. Relevant methodology
add(value): Adds a value to the Set object. If the value already exists, nothing is done.
delete(value): Delete a value from the Set object. If the value exists, it is deleted and true is returned; otherwise, false is returned.
has(value): Returns a boolean indicating whether the Set object contains the specified value.
clear(): Clear the Set object, removing all elements.
III. Basic use
let setData = new Set(); // Adding Elements setData .add(1); setData .add(2); setData .add(3); (setData); // setData { 1, 2 ,3 } // Delete element setData.delete(2); (setData); // Set { 1, 3 } // Checking for the existence of an element ((1)); // true ((4)); // false // Iterate over elements (value => (value)); // Output. // 1 // 3 // Empty the collection (); (); // Output: 0, because the set is empty //Initialize a Set by passing in an iterable object (such as an array) directly when creating the Set: let set = new Set([1, 2, 2, 3, 4, 4]); //Simple array de-duplication (set); // Set { 1, 2, 3, 4 }