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array.prototype.flatMap Set good usage scenario example
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| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <meta charset="utf-8"> | |
| <meta name="viewport" content="width=device-width"> | |
| <title>JS Bin</title> | |
| </head> | |
| <body> | |
| <script id="jsbin-javascript"> | |
| const friends = [{ | |
| name: 'Anna', | |
| books: ['Bible', 'Harry Potter'], | |
| age: 21 | |
| }, { | |
| name: 'Bob', | |
| books: ['War and peace', 'Romeo and Juliet'], | |
| age: 26 | |
| }, { | |
| name: 'Alice', | |
| books: ['The Lord of the Rings', 'Bible'], | |
| age: 18 | |
| }]; | |
| var allBooks1 = friends.reduce((prev, curr) => [...prev, ...curr.books], []).reduce((init, current) => { | |
| if (init.indexOf(current) < 0) { | |
| init.push(current); | |
| } | |
| return init; | |
| }, []); | |
| const allBooks2 = [...new Set(friends.flatMap(friend => friend.books))] | |
| console.log(allBooks1); | |
| console.log(allBooks2); | |
| </script> | |
| <script id="jsbin-source-javascript" type="text/javascript"> | |
| const friends = [{ | |
| name: 'Anna', | |
| books: ['Bible', 'Harry Potter'], | |
| age: 21 | |
| }, { | |
| name: 'Bob', | |
| books: ['War and peace', 'Romeo and Juliet'], | |
| age: 26 | |
| }, { | |
| name: 'Alice', | |
| books: ['The Lord of the Rings', 'Bible'], | |
| age: 18 | |
| }]; | |
| var allBooks1 = friends.reduce((prev, curr) => [...prev, ...curr.books], []).reduce((init, current) => { | |
| if (init.indexOf(current) < 0) { | |
| init.push(current); | |
| } | |
| return init; | |
| }, []); | |
| const allBooks2 = [...new Set(friends.flatMap(friend => friend.books))] | |
| console.log(allBooks1); | |
| console.log(allBooks2);</script></body> | |
| </html> |
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| const friends = [{ | |
| name: 'Anna', | |
| books: ['Bible', 'Harry Potter'], | |
| age: 21 | |
| }, { | |
| name: 'Bob', | |
| books: ['War and peace', 'Romeo and Juliet'], | |
| age: 26 | |
| }, { | |
| name: 'Alice', | |
| books: ['The Lord of the Rings', 'Bible'], | |
| age: 18 | |
| }]; | |
| var allBooks1 = friends.reduce((prev, curr) => [...prev, ...curr.books], []).reduce((init, current) => { | |
| if (init.indexOf(current) < 0) { | |
| init.push(current); | |
| } | |
| return init; | |
| }, []); | |
| const allBooks2 = [...new Set(friends.flatMap(friend => friend.books))] | |
| console.log(allBooks1); | |
| console.log(allBooks2); |
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