codepedia.de

# Maps & Sets

  • not so important…
  • you can allways convert to an array with Array.from
Arrays Sets Maps
Store (nested) data of any kind and length Store (nested) data of any kind and length Store key-value data of any kind and length. Any Key-values are allowed
Iterale, many special array-methods available iterable, also some special set methods availabe iterable, also some special map methods availabe
Order is guranteed. Duplicates are allowed. Zero-based index to access elements Order is NOT guaranteed. Duplicates are NOT allowed. No index-based access Order is guaranteed. Duplicates are NOT allowed. Key-based access

# Sets

  • no duplicates
  • can be useful to manage unique data
# Create:
  • const mySet = new Set(['Hi', 'from', 'set!']);

  • to get a value

    mySet.has('Hi')
# .add

  • add a value

    mySet.add("yeah")
    • if you add a value that alredy exist, it will not be added. Values are unique in sets
# .entries()
  • returns an iterable of arrays with the value twice (to be the same as the -tentries-mehod of maps)
# .values()
  • retuns the values (iteratable)
# .delete('Hi')
  • delete a value
image-20220201163000856

# Maps

  • can have anything as a key (eg. an object)
  • key-value-pairs
  • can have anything as a key
  • order is guarented (unlike in objects)
  • for example to attach extra information to an object
const person1 = { name: 'Max' };
const person2 = { name: 'Manuel' };

const personData = new Map([[person1, [{ date: 'yesterday', price: 10 }]]]);
image-20220202083346928

I.e. you don't have to do:

const person1 = {id: 'p1', ...};
const personData = { p1: [ ... ]};
console.log(personDate[person.id])

get data:

console.log(personData.get(person1));

set data

personData.set(person2, [{ date: 'two weeks ago', price: 100 }]);

output all information of the map - for...of

for (const [key, value] of personData.entries()) {
  console.log(key, value); // .entries() returns an array with key/value
} 

for (const key of personData.keys()) {
  console.log(key);
}

for (const value of personData.values()) {
  console.log(value);
}

methods & properties:

image-20220202084111338

# WeakSet

  • data has to be an object
  • only has add, delete and has -methods

you can clear the weak-set and all the objects will be garbage-collected

// ... some operations
person = null;

# WeakMap

  • also for garbage-collection
const personData = new WeakMap();
personData.set(person, 'Extra info!');

person = null;

console.log(personData);

← Destructuring →