kode javascript

Apa gunanya objek peta dalam javascript?

JavaScript menyediakan metode map() untuk membuat fungsi peta untuk berinteraksi dengan properti objek. Ini mengulangi semua atribut objek dengan memanfaatkan nilai kunci. Selain itu, peta. metode set() digunakan untuk menetapkan atribut objek. Apalagi Obyek. entri() mengembalikan semua atribut objek setelah membuat fungsi peta di JavaScript. Artikel ini mendemonstrasikan pembuatan fungsi peta untuk objek dan menampilkan semua atribut objek di jendela konsol

Peta adalah kumpulan item data yang diberi kunci, seperti let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1235. Tetapi perbedaan utamanya adalah let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 123_3 mengizinkan kunci jenis apa pun

Metode dan properti adalah

let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 123_7 – membuat peta
let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1238 – menyimpan nilai dengan kunci
let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 123_9 – mengembalikan nilai dengan kunci, let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1230 jika let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1231 tidak ada di peta
let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1232 – mengembalikan let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1233 jika let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1231 ada, let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1235 sebaliknya
let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1236 – menghapus elemen (pasangan kunci/nilai) dengan kunci
let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1237 – menghapus semuanya dari peta
let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1238 – mengembalikan jumlah elemen saat ini

Contohnya

let map = new Map(); map.set('1', 'str1'); // a string key map.set(1, 'num1'); // a numeric key map.set(true, 'bool1'); // a boolean key // remember the regular Object? it would convert keys to string // Map keeps the type, so these two are different: alert( map.get(1) ); // 'num1' alert( map.get('1') ); // 'str1' alert( map.size ); // 3

Seperti yang bisa kita lihat, tidak seperti objek, kunci tidak diubah menjadi string. Semua jenis kunci dimungkinkan

Meskipun let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 123_9 juga berfungsi, mis. g. kita dapat mengatur map.set('1', 'str1') .set(1, 'num1') .set(true, 'bool1');_2, ini memperlakukan map.set('1', 'str1') .set(1, 'num1') .set(true, 'bool1');3 sebagai objek JavaScript biasa, jadi ini menyiratkan semua batasan yang sesuai (hanya kunci string/simbol dan sebagainya)

Jadi kita harus menggunakan metode ________18______3. map.set('1', 'str1') .set(1, 'num1') .set(true, 'bool1');5, map.set('1', 'str1') .set(1, 'num1') .set(true, 'bool1');6 dan seterusnya

Peta juga dapat menggunakan objek sebagai kunci

Contohnya

Menggunakan objek sebagai kunci adalah salah satu fitur let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1233 yang paling menonjol dan penting. Hal yang sama tidak dihitung untuk let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1235. String sebagai kunci di let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1235 baik-baik saja, tetapi kita tidak dapat menggunakan let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1235 lain sebagai kunci di let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1235

Mari mencoba

Karena let recipeMap = new Map([ ['cucumber', 500], ['tomatoes', 350], ['onion', 50] ]); // iterate over keys (vegetables) for (let vegetable of recipeMap.keys()) { alert(vegetable); // cucumber, tomatoes, onion } // iterate over values (amounts) for (let amount of recipeMap.values()) { alert(amount); // 500, 350, 50 } // iterate over [key, value] entries for (let entry of recipeMap) { // the same as of recipeMap.entries() alert(entry); // cucumber,500 (and so on) }_2 adalah sebuah objek, ia mengonversi semua let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1235 kunci, seperti let recipeMap = new Map([ ['cucumber', 500], ['tomatoes', 350], ['onion', 50] ]); // iterate over keys (vegetables) for (let vegetable of recipeMap.keys()) { alert(vegetable); // cucumber, tomatoes, onion } // iterate over values (amounts) for (let amount of recipeMap.values()) { alert(amount); // 500, 350, 50 } // iterate over [key, value] entries for (let entry of recipeMap) { // the same as of recipeMap.entries() alert(entry); // cucumber,500 (and so on) }4 dan let recipeMap = new Map([ ['cucumber', 500], ['tomatoes', 350], ['onion', 50] ]); // iterate over keys (vegetables) for (let vegetable of recipeMap.keys()) { alert(vegetable); // cucumber, tomatoes, onion } // iterate over values (amounts) for (let amount of recipeMap.values()) { alert(amount); // 500, 350, 50 } // iterate over [key, value] entries for (let entry of recipeMap) { // the same as of recipeMap.entries() alert(entry); // cucumber,500 (and so on) }5 di atas, menjadi string yang sama let recipeMap = new Map([ ['cucumber', 500], ['tomatoes', 350], ['onion', 50] ]); // iterate over keys (vegetables) for (let vegetable of recipeMap.keys()) { alert(vegetable); // cucumber, tomatoes, onion } // iterate over values (amounts) for (let amount of recipeMap.values()) { alert(amount); // 500, 350, 50 } // iterate over [key, value] entries for (let entry of recipeMap) { // the same as of recipeMap.entries() alert(entry); // cucumber,500 (and so on) }6. Jelas bukan yang kita inginkan

Bagaimana let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 123_3 membandingkan kunci

Untuk menguji kunci kesetaraan, let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1233 menggunakan algoritme. Ini kira-kira sama dengan persamaan ketat let recipeMap = new Map([ ['cucumber', 500], ['tomatoes', 350], ['onion', 50] ]); // iterate over keys (vegetables) for (let vegetable of recipeMap.keys()) { alert(vegetable); // cucumber, tomatoes, onion } // iterate over values (amounts) for (let amount of recipeMap.values()) { alert(amount); // 500, 350, 50 } // iterate over [key, value] entries for (let entry of recipeMap) { // the same as of recipeMap.entries() alert(entry); // cucumber,500 (and so on) }9, tetapi perbedaannya adalah bahwa // runs the function for each (key, value) pair recipeMap.forEach( (value, key, map) => { alert(`${key}: ${value}`); // cucumber: 500 etc });0 dianggap sama dengan // runs the function for each (key, value) pair recipeMap.forEach( (value, key, map) => { alert(`${key}: ${value}`); // cucumber: 500 etc });0. Jadi // runs the function for each (key, value) pair recipeMap.forEach( (value, key, map) => { alert(`${key}: ${value}`); // cucumber: 500 etc });_0 dapat digunakan sebagai kunci juga

Algoritme ini tidak dapat diubah atau disesuaikan

Merantai

Setiap // runs the function for each (key, value) pair recipeMap.forEach( (value, key, map) => { alert(`${key}: ${value}`); // cucumber: 500 etc });_3 panggilan mengembalikan peta itu sendiri, sehingga kita dapat "menghubungkan" panggilan

map.set('1', 'str1') .set(1, 'num1') .set(true, 'bool1');

Untuk mengulang map.set('1', 'str1') .set(1, 'num1') .set(true, 'bool1');_3, ada 3 metode

// runs the function for each (key, value) pair recipeMap.forEach( (value, key, map) => { alert(`${key}: ${value}`); // cucumber: 500 etc });5 – mengembalikan iterable untuk kunci,
// runs the function for each (key, value) pair recipeMap.forEach( (value, key, map) => { alert(`${key}: ${value}`); // cucumber: 500 etc });6 – mengembalikan iterable untuk nilai,
// runs the function for each (key, value) pair recipeMap.forEach( (value, key, map) => { alert(`${key}: ${value}`); // cucumber: 500 etc });7 – mengembalikan iterable untuk entri // runs the function for each (key, value) pair recipeMap.forEach( (value, key, map) => { alert(`${key}: ${value}`); // cucumber: 500 etc });8, ini digunakan secara default di // runs the function for each (key, value) pair recipeMap.forEach( (value, key, map) => { alert(`${key}: ${value}`); // cucumber: 500 etc });9

Contohnya

Urutan penyisipan digunakan

Iterasi berjalan dalam urutan yang sama dengan nilai yang dimasukkan. let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1233 mempertahankan urutan ini, tidak seperti let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1235 biasa

Selain itu, let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1233 memiliki metode // array of [key, value] pairs let map = new Map([ ['1', 'str1'], [1, 'num1'], [true, 'bool1'] ]); alert( map.get('1') ); // str13 bawaan, mirip dengan // array of [key, value] pairs let map = new Map([ ['1', 'str1'], [1, 'num1'], [true, 'bool1'] ]); alert( map.get('1') ); // str14

// runs the function for each (key, value) pair recipeMap.forEach( (value, key, map) => { alert(`${key}: ${value}`); // cucumber: 500 etc });

Saat let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 123_3 dibuat, kita dapat melewatkan array (atau iterable lainnya) dengan pasangan kunci/nilai untuk inisialisasi, seperti ini

// array of [key, value] pairs let map = new Map([ ['1', 'str1'], [1, 'num1'], [true, 'bool1'] ]); alert( map.get('1') ); // str1

Jika kita memiliki objek biasa, dan kita ingin membuat let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1233 darinya, maka kita dapat menggunakan metode Object bawaan. entri(obj) yang mengembalikan array pasangan kunci/nilai untuk objek persis dalam format itu

Jadi kita bisa membuat peta dari objek seperti ini

let obj = { name: "John", age: 30 }; let map = new Map(Object.entries(obj)); alert( map.get('name') ); // John

Di sini, // array of [key, value] pairs let map = new Map([ ['1', 'str1'], [1, 'num1'], [true, 'bool1'] ]); alert( map.get('1') ); // str1_7 mengembalikan larik pasangan kunci/nilai. // array of [key, value] pairs let map = new Map([ ['1', 'str1'], [1, 'num1'], [true, 'bool1'] ]); alert( map.get('1') ); // str1_8. Itulah yang dibutuhkan let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1233

Kami baru saja melihat cara membuat let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1233 dari objek biasa dengan let obj = { name: "John", age: 30 }; let map = new Map(Object.entries(obj)); alert( map.get('name') ); // John1

Ada let obj = { name: "John", age: 30 }; let map = new Map(Object.entries(obj)); alert( map.get('name') ); // John2 metode yang sebaliknya. diberikan array // runs the function for each (key, value) pair recipeMap.forEach( (value, key, map) => { alert(`${key}: ${value}`); // cucumber: 500 etc });8 pasangan, itu membuat objek dari mereka

let prices = Object.fromEntries([ ['banana', 1], ['orange', 2], ['meat', 4] ]); // now prices = { banana: 1, orange: 2, meat: 4 } alert(prices.orange); // 2

Kita dapat menggunakan let obj = { name: "John", age: 30 }; let map = new Map(Object.entries(obj)); alert( map.get('name') ); // John_2 untuk mendapatkan objek polos dari let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1233

E. g. kami menyimpan data dalam let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1233, tetapi kami harus meneruskannya ke kode pihak ke-3 yang mengharapkan objek biasa

Ini dia

let map = new Map(); map.set('banana', 1); map.set('orange', 2); map.set('meat', 4); let obj = Object.fromEntries(map.entries()); // make a plain object (*) // done! // obj = { banana: 1, orange: 2, meat: 4 } alert(obj.orange); // 2

Panggilan ke // runs the function for each (key, value) pair recipeMap.forEach( (value, key, map) => { alert(`${key}: ${value}`); // cucumber: 500 etc });7 mengembalikan iterable pasangan kunci/nilai, persis dalam format yang tepat untuk let obj = { name: "John", age: 30 }; let map = new Map(Object.entries(obj)); alert( map.get('name') ); // John2

Kita juga bisa membuat garis let obj = { name: "John", age: 30 }; let map = new Map(Object.entries(obj)); alert( map.get('name') ); // John_9 lebih pendek

Itu sama, karena let obj = { name: "John", age: 30 }; let map = new Map(Object.entries(obj)); alert( map.get('name') ); // John_2 mengharapkan objek yang dapat diubah sebagai argumen. Belum tentu array. Dan iterasi standar untuk map.set('1', 'str1') .set(1, 'num1') .set(true, 'bool1');3 mengembalikan pasangan kunci/nilai yang sama dengan // runs the function for each (key, value) pair recipeMap.forEach( (value, key, map) => { alert(`${key}: ${value}`); // cucumber: 500 etc });7. Jadi kami mendapatkan objek biasa dengan kunci/nilai yang sama dengan map.set('1', 'str1') .set(1, 'num1') .set(true, 'bool1');3

let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1234 adalah kumpulan tipe khusus – “himpunan nilai” (tanpa kunci), di mana setiap nilai hanya dapat muncul sekali

Metode utamanya adalah

let prices = Object.fromEntries([ ['banana', 1], ['orange', 2], ['meat', 4] ]); // now prices = { banana: 1, orange: 2, meat: 4 } alert(prices.orange); // 25 – membuat set, dan jika objek let prices = Object.fromEntries([ ['banana', 1], ['orange', 2], ['meat', 4] ]); // now prices = { banana: 1, orange: 2, meat: 4 } alert(prices.orange); // 26 disediakan (biasanya array), menyalin nilai darinya ke dalam set
let prices = Object.fromEntries([ ['banana', 1], ['orange', 2], ['meat', 4] ]); // now prices = { banana: 1, orange: 2, meat: 4 } alert(prices.orange); // 27 – menambahkan nilai, mengembalikan set itu sendiri
let prices = Object.fromEntries([ ['banana', 1], ['orange', 2], ['meat', 4] ]); // now prices = { banana: 1, orange: 2, meat: 4 } alert(prices.orange); // 28 – menghapus nilai, mengembalikan let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1233 jika let map = new Map(); map.set('banana', 1); map.set('orange', 2); map.set('meat', 4); let obj = Object.fromEntries(map.entries()); // make a plain object (*) // done! // obj = { banana: 1, orange: 2, meat: 4 } alert(obj.orange); // 20 ada pada saat panggilan, jika tidak let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1235
let map = new Map(); map.set('banana', 1); map.set('orange', 2); map.set('meat', 4); let obj = Object.fromEntries(map.entries()); // make a plain object (*) // done! // obj = { banana: 1, orange: 2, meat: 4 } alert(obj.orange); // 22 – mengembalikan let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1233 jika nilainya ada di himpunan, jika tidak let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1235
let map = new Map(); map.set('banana', 1); map.set('orange', 2); map.set('meat', 4); let obj = Object.fromEntries(map.entries()); // make a plain object (*) // done! // obj = { banana: 1, orange: 2, meat: 4 } alert(obj.orange); // 25 – menghapus semuanya dari set
let map = new Map(); map.set('banana', 1); map.set('orange', 2); map.set('meat', 4); let obj = Object.fromEntries(map.entries()); // make a plain object (*) // done! // obj = { banana: 1, orange: 2, meat: 4 } alert(obj.orange); // 26 – adalah jumlah elemen

Fitur utamanya adalah panggilan berulang let prices = Object.fromEntries([ ['banana', 1], ['orange', 2], ['meat', 4] ]); // now prices = { banana: 1, orange: 2, meat: 4 } alert(prices.orange); // 27 dengan nilai yang sama tidak melakukan apa-apa. Itulah alasan mengapa setiap nilai muncul di let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1234 hanya sekali

Misalnya, ada pengunjung yang datang, dan kami ingin mengingat semua orang. Tetapi kunjungan berulang tidak boleh mengarah pada duplikat. Seorang pengunjung harus "dihitung" hanya sekali

Alternatif untuk let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 123_4 bisa berupa larik pengguna, dan kode untuk memeriksa duplikat pada setiap penyisipan menggunakan arr. Temukan. Tetapi kinerjanya akan jauh lebih buruk, karena metode ini menelusuri seluruh larik yang memeriksa setiap elemen. let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1234 jauh lebih baik dioptimalkan secara internal untuk pemeriksaan keunikan

Kita dapat mengulang satu set dengan ________38______9 atau menggunakan // array of [key, value] pairs let map = new Map([ ['1', 'str1'], [1, 'num1'], [true, 'bool1'] ]); alert( map.get('1') ); // str13

Perhatikan hal yang lucu. Fungsi panggilan balik yang diteruskan dalam // array of [key, value] pairs let map = new Map([ ['1', 'str1'], [1, 'num1'], [true, 'bool1'] ]); alert( map.get('1') ); // str13 memiliki 3 argumen. a let map = new Map(); map.set('banana', 1); map.set('orange', 2); map.set('meat', 4); let obj = Object.fromEntries(map.entries()); // make a plain object (*) // done! // obj = { banana: 1, orange: 2, meat: 4 } alert(obj.orange); // 20, lalu nilai yang sama let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 12306, lalu objek target. Memang, nilai yang sama muncul di argumen dua kali

Itu untuk kompatibilitas dengan let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 123_3 di mana panggilan balik berlalu // array of [key, value] pairs let map = new Map([ ['1', 'str1'], [1, 'num1'], [true, 'bool1'] ]); alert( map.get('1') ); // str13 memiliki tiga argumen. Terlihat agak aneh, pasti. Tapi ini dapat membantu mengganti let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 123_3 dengan let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1234 dalam kasus tertentu dengan mudah, dan sebaliknya

Metode yang sama let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 123_3 untuk iterator juga didukung

let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 123_12 – mengembalikan objek iterable untuk nilai,
let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 123_13 – sama seperti let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 12312, untuk kompatibilitas dengan let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1233,
let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 123_16 – mengembalikan objek iterable untuk entri let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 12317, ada untuk kompatibilitas dengan let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1233

Metode dan properti

let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 123_20 – membuat peta, dengan opsional let prices = Object.fromEntries([ ['banana', 1], ['orange', 2], ['meat', 4] ]); // now prices = { banana: 1, orange: 2, meat: 4 } alert(prices.orange); // 26 (e. g. array) dari let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 123_22 pasang untuk inisialisasi
let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1238 – menyimpan nilai dengan kunci, mengembalikan peta itu sendiri
let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 123_9 – mengembalikan nilai dengan kunci, let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1230 jika let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1231 tidak ada di peta
let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1232 – mengembalikan let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1233 jika let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1231 ada, let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1235 sebaliknya
let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1236 – menghapus elemen dengan kunci, mengembalikan let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1233 jika let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1231 ada pada saat panggilan, jika tidak let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1235
let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1237 – menghapus semuanya dari peta
let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1238 – mengembalikan jumlah elemen saat ini

Perbedaan dari let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 123 biasa5

Kunci apa saja, objek bisa menjadi kunci
Metode nyaman tambahan, properti let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 12338

Metode dan properti

let prices = Object.fromEntries([ ['banana', 1], ['orange', 2], ['meat', 4] ]); // now prices = { banana: 1, orange: 2, meat: 4 } alert(prices.orange); // 25 – membuat set, dengan opsional let prices = Object.fromEntries([ ['banana', 1], ['orange', 2], ['meat', 4] ]); // now prices = { banana: 1, orange: 2, meat: 4 } alert(prices.orange); // 26 (e. g. array) nilai untuk inisialisasi
let prices = Object.fromEntries([ ['banana', 1], ['orange', 2], ['meat', 4] ]); // now prices = { banana: 1, orange: 2, meat: 4 } alert(prices.orange); // 27 – menambahkan nilai (tidak melakukan apa-apa jika let map = new Map(); map.set('banana', 1); map.set('orange', 2); map.set('meat', 4); let obj = Object.fromEntries(map.entries()); // make a plain object (*) // done! // obj = { banana: 1, orange: 2, meat: 4 } alert(obj.orange); // 20 ada), mengembalikan himpunan itu sendiri
let prices = Object.fromEntries([ ['banana', 1], ['orange', 2], ['meat', 4] ]); // now prices = { banana: 1, orange: 2, meat: 4 } alert(prices.orange); // 28 – menghapus nilai, mengembalikan let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1233 jika let map = new Map(); map.set('banana', 1); map.set('orange', 2); map.set('meat', 4); let obj = Object.fromEntries(map.entries()); // make a plain object (*) // done! // obj = { banana: 1, orange: 2, meat: 4 } alert(obj.orange); // 20 ada pada saat panggilan, jika tidak let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1235
let map = new Map(); map.set('banana', 1); map.set('orange', 2); map.set('meat', 4); let obj = Object.fromEntries(map.entries()); // make a plain object (*) // done! // obj = { banana: 1, orange: 2, meat: 4 } alert(obj.orange); // 22 – mengembalikan let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1233 jika nilainya ada di himpunan, jika tidak let john = { name: "John" }; let ben = { name: "Ben" }; let visitsCountObj = {}; // try to use an object visitsCountObj[ben] = 234; // try to use ben object as the key visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced // That's what got written! alert( visitsCountObj["[object Object]"] ); // 1235
let map = new Map(); map.set('banana', 1); map.set('orange', 2); map.set('meat', 4); let obj = Object.fromEntries(map.entries()); // make a plain object (*) // done! // obj = { banana: 1, orange: 2, meat: 4 } alert(obj.orange); // 25 – menghapus semuanya dari set
let map = new Map(); map.set('banana', 1); map.set('orange', 2); map.set('meat', 4); let obj = Object.fromEntries(map.entries()); // make a plain object (*) // done! // obj = { banana: 1, orange: 2, meat: 4 } alert(obj.orange); // 26 – adalah jumlah elemen

Iterasi di atas let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1233 dan let john = { name: "John" }; // for every user, let's store their visits count let visitsCountMap = new Map(); // john is the key for the map visitsCountMap.set(john, 123); alert( visitsCountMap.get(john) ); // 1234 selalu dalam urutan penyisipan, jadi kami tidak dapat mengatakan bahwa koleksi ini tidak diurutkan, tetapi kami tidak dapat menyusun ulang elemen atau langsung mendapatkan elemen berdasarkan nomornya

Haruskah saya menggunakan peta atau objek dalam JavaScript?

Dalam Objek, tipe data bidang kunci dibatasi untuk bilangan bulat, string, dan simbol. Sedangkan di Peta, bidang kunci dapat berupa tipe data apa saja (bilangan bulat, larik, bahkan objek. ) Di Peta, urutan asli elemen dipertahankan. Ini tidak benar dalam kasus objek.

Apa yang dimaksud dengan memetakan objek?

Peta objek adalah aset uji yang berisi item yang mengaitkan nama logis (alias) dengan kontrol atau jendela, bukan penentu lokasi kontrol atau jendela. Once a control is registered in an object map asset, all references to it in scripts are made by its alias, rather than by its actual locator name.

Untuk apa metode peta () digunakan?

Fungsi map() digunakan untuk mengulangi larik dan memanipulasi atau mengubah item data . Di React, fungsi map() paling umum digunakan untuk merender daftar data ke DOM.

Bagaimana cara mendapatkan nilai dari objek peta di JavaScript?

Metode get() mengembalikan elemen tertentu dari objek Map . Jika nilai yang terkait dengan kunci yang disediakan adalah sebuah objek, maka Anda akan mendapatkan referensi ke objek tersebut dan setiap perubahan yang dilakukan pada objek tersebut akan secara efektif memodifikasinya di dalam objek Peta.

Apa gunanya objek peta dalam javascript?

Haruskah saya menggunakan peta atau objek dalam JavaScript?

Apa yang dimaksud dengan memetakan objek?

Untuk apa metode peta () digunakan?

Bagaimana cara mendapatkan nilai dari objek peta di JavaScript?

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