通过其属性值在 Map 中查找元素

Question

I have a Map of objects:

const myMap = new Map() 

myMap.set(123, {
  name: 'Lorem',
  elements: {
    books: ['book#1', 'book#2', 'book#3']
  }
})

myMap.set(521, {
  name: 'Ipsum',
  elements: {
    books: ['book#42', 'book#13', 'book#42']
 }
})

And at some point, I will need to find an element in Map, which contain book#42 in elements.books array. How Can I do it properly?

Answer 1

You can loop through the Map() with the for...of statement. This statement exposes each entry, which is a key-value pair. The value is where you should check for your book. Specifically in the elements.books array. When you found your book, return the key of the entry. Now you have the key to select the correct entry from the Map() .

 const myMap = new Map() myMap.set(123, { name: 'Lorem', elements: { books: ['book#1', 'book#2', 'book#3'] } }); myMap.set(521, { name: 'Ipsum', elements: { books: ['book#42', 'book#13', 'book#42'] } }); const findKeyOfBook = (book, map) => { let result = null; for (const [key, value] of map) { if (value.elements.books.includes(book)) { result = key; } } return result; }; const key = findKeyOfBook('book#42', myMap); const entryWithBook = myMap.get(key); console.log(entryWithBook);

Answer 2

You can do simply by doing this using entries :

 const myMap = new Map() myMap.set(123, { name: 'Lorem', elements: { books: ['book#1', 'book#2', 'book#3'] } }) myMap.set(521, { name: 'Ipsum', elements: { books: ['book#42', 'book#13', 'book#42'] } }) for([key,value] of myMap.entries()){ if(value.elements.books.includes('book#42')){ console.log("Found value",key,value) } }

Answer 3

You can convert the iterator returned by Map.prototype.values() into an actual array (with the spread ( ... ) syntax or Array.from() ) and then use Array.prototype.find()

 const myMap = new Map() myMap.set(123, { name: 'Lorem', elements: { books: ['book#1', 'book#2', 'book#3'] } }) myMap.set(521, { name: 'Ipsum', elements: { books: ['book#42', 'book#13', 'book#42'] } }) const findWithSpread = function(map, book) { return [...map.values()].find(entry => entry.elements.books.includes(book)); //return Array.from(map.values()).find(...); } const element = findWithSpread(myMap, "book#42"); console.log(element);