Cara menggunakan latihan pengurangan javascript

Peredam berjalan melalui elemen-demi-elemen array, pada setiap langkah menambahkan nilai array saat ini ke hasil dari langkah sebelumnya (hasil ini adalah jumlah berjalan dari semua langkah sebelumnya) — sampai tidak ada lagi elemen untuk ditambahkan

// Arrow function reduce((accumulator, currentValue) => { /* … */ }) reduce((accumulator, currentValue, currentIndex) => { /* … */ }) reduce((accumulator, currentValue, currentIndex, array) => { /* … */ }) reduce((accumulator, currentValue) => { /* … */ }, initialValue) reduce((accumulator, currentValue, currentIndex) => { /* … */ }, initialValue) reduce((accumulator, currentValue, currentIndex, array) => { /* … */ }, initialValue) // Callback function reduce(callbackFn) reduce(callbackFn, initialValue) // Inline callback function reduce(function (accumulator, currentValue) { /* … */ }) reduce(function (accumulator, currentValue, currentIndex) { /* … */ }) reduce(function (accumulator, currentValue, currentIndex, array) { /* … */ }) reduce(function (accumulator, currentValue) { /* … */ }, initialValue) reduce(function (accumulator, currentValue, currentIndex) { /* … */ }, initialValue) reduce(function (accumulator, currentValue, currentIndex, array) { /* … */ }, initialValue)

const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError _7

Fungsi untuk mengeksekusi setiap elemen dalam array. Nilai pengembaliannya menjadi nilai parameter const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 8 pada pemanggilan const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 7 berikutnya. Untuk pemanggilan terakhir, nilai yang dikembalikan menjadi nilai yang dikembalikan const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 5

Fungsi tersebut dipanggil dengan argumen berikut

Nilai yang dihasilkan dari panggilan sebelumnya ke const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 7. Pada panggilan pertama, const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); _3 jika ditentukan, jika tidak, nilai const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); 4

Nilai elemen saat ini. Pada panggilan pertama, nilai const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); _4 jika const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); 3 ditentukan, jika tidak, nilai const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); 8

Posisi indeks const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); _5 dalam larik. Pada panggilan pertama, [15, 16, 17, 18, 19].reduce( (accumulator, currentValue) => accumulator + currentValue, 10, ); 1 jika const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); 3 ditentukan, jika tidak [15, 16, 17, 18, 19].reduce( (accumulator, currentValue) => accumulator + currentValue, 10, ); 3

Array const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError _5 dipanggil

Nilai yang const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError _8 diinisialisasi saat pertama kali callback dipanggil. Jika const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); _3 ditentukan, const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 7 mulai mengeksekusi dengan nilai pertama dalam larik sebagai const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); 5. Jika const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); _3 tidak ditentukan, const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 8 diinisialisasi ke nilai pertama dalam larik, dan const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 7 mulai mengeksekusi dengan nilai kedua dalam larik sebagai const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); 5. Dalam hal ini, jika array kosong (sehingga tidak ada nilai pertama yang dikembalikan sebagai const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 8), kesalahan akan terjadi

Nilai yang dihasilkan dari menjalankan fungsi panggilan balik "peredam" hingga penyelesaian seluruh larik

const objects = [{ x: 1 }, { x: 2 }, { x: 3 }]; const sum = objects.reduce( (accumulator, currentValue) => accumulator + currentValue.x, 0, ); console.log(sum); // 6 _6

Larik tidak berisi elemen dan const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); _3 tidak disediakan

Metode const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 5 adalah sebuah. Ini menjalankan fungsi panggilan balik "peredam" pada semua elemen dalam larik, dalam urutan indeks naik, dan mengakumulasikannya menjadi satu nilai. Setiap kali, nilai pengembalian const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError _7 diteruskan ke const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 7 lagi pada pemanggilan berikutnya sebagai const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 8. Nilai akhir dari const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 8 (yang merupakan nilai yang dikembalikan dari const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 7 pada iterasi terakhir dari array) menjadi nilai kembalian dari const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 5

const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 7 dipanggil hanya untuk indeks array yang telah menetapkan nilai. Itu tidak dipanggil untuk slot kosong

Tidak seperti yang lain, const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 5 tidak menerima argumen const flattened = [ [0, 1], [2, 3], [4, 5], ].reduce((accumulator, currentValue) => accumulator.concat(currentValue), []); // flattened is [0, 1, 2, 3, 4, 5] 7. const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 7 selalu dipanggil dengan const flattened = [ [0, 1], [2, 3], [4, 5], ].reduce((accumulator, currentValue) => accumulator.concat(currentValue), []); // flattened is [0, 1, 2, 3, 4, 5] 9 sebagai const names = ["Alice", "Bob", "Tiff", "Bruce", "Alice"]; const countedNames = names.reduce((allNames, name) => { const currCount = allNames[name] ?? 0; return { ...allNames, [name]: currCount + 1, }; }, {}); // countedNames is: // { 'Alice': 2, 'Bob': 1, 'Tiff': 1, 'Bruce': 1 } 0, yang diganti dengan const names = ["Alice", "Bob", "Tiff", "Bruce", "Alice"]; const countedNames = names.reduce((allNames, name) => { const currCount = allNames[name] ?? 0; return { ...allNames, [name]: currCount + 1, }; }, {}); // countedNames is: // { 'Alice': 2, 'Bob': 1, 'Tiff': 1, 'Bruce': 1 } 1 jika const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 7 tidak ketat

const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 5 adalah konsep sentral dalam pemrograman fungsional, di mana tidak mungkin mengubah nilai apa pun, jadi untuk mengakumulasi semua nilai dalam array, seseorang harus mengembalikan nilai akumulator baru pada setiap iterasi. Konvensi ini menyebar ke const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 5 JavaScript. Anda harus menggunakan metode penyebaran atau penyalinan lainnya jika memungkinkan untuk membuat larik dan objek baru sebagai akumulator, daripada memutasikan yang sudah ada. Jika Anda memutuskan untuk mengubah akumulator alih-alih menyalinnya, ingatlah untuk tetap mengembalikan objek yang dimodifikasi dalam panggilan balik, atau iterasi berikutnya akan menerima undefined

const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 5 tidak mengubah array yang dipanggil, tetapi fungsi yang disediakan sebagai const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 7 dapat. Perhatikan, bagaimanapun, bahwa panjang array disimpan sebelum pemanggilan pertama dari const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 7. Karena itu

• const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 7 tidak akan mengunjungi elemen apa pun yang ditambahkan melebihi panjang awal array saat panggilan ke const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 5 dimulai
• Perubahan pada indeks yang sudah dikunjungi tidak menyebabkan const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 7 dipanggil lagi
• Jika ada elemen array yang belum dikunjungi diubah oleh const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 7, nilainya diteruskan ke const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 7 akan menjadi nilai pada saat elemen dikunjungi. Elemen yang dihapus tidak dikunjungi

Peringatan. Modifikasi bersamaan dari jenis yang dijelaskan di atas sering menyebabkan kode yang sulit dipahami dan umumnya harus dihindari (kecuali dalam kasus khusus)

Metode const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 5 adalah. Itu hanya mengharapkan nilai const names = ["Alice", "Bob", "Tiff", "Bruce", "Alice"]; const countedNames = names.reduce((allNames, name) => { const currCount = allNames[name] ?? 0; return { ...allNames, [name]: currCount + 1, }; }, {}); // countedNames is: // { 'Alice': 2, 'Bob': 1, 'Tiff': 1, 'Bruce': 1 } _0 memiliki properti const people = [ { name: "Alice", age: 21 }, { name: "Max", age: 20 }, { name: "Jane", age: 20 }, ]; function groupBy(objectArray, property) { return objectArray.reduce((acc, obj) => { const key = obj[property]; const curGroup = acc[key] ?? []; return { ...acc, [key]: [...curGroup, obj] }; }, {}); } const groupedPeople = groupBy(people, "age"); console.log(groupedPeople); // { // 20: [ // { name: 'Max', age: 20 }, // { name: 'Jane', age: 20 } // ], // 21: [{ name: 'Alice', age: 21 }] // } 5 dan properti dengan kunci bilangan bulat

Fungsi rekursif seperti const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 5 bisa sangat berguna, tetapi terkadang sulit dipahami, terutama bagi pengembang JavaScript yang kurang berpengalaman. Jika kode menjadi lebih jelas saat menggunakan metode larik lainnya, pengembang harus mempertimbangkan tradeoff keterbacaan terhadap manfaat lain menggunakan const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 5. Dalam kasus di mana const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 5 adalah pilihan terbaik, dokumentasi dan penamaan variabel semantik dapat membantu mengurangi kelemahan keterbacaan

Jika array hanya memiliki satu elemen (terlepas dari posisinya) dan tidak ada const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); 3 yang disediakan, atau jika const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); 3 disediakan tetapi array kosong, nilai tunggal akan dikembalikan tanpa memanggil const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 7

Jika const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); _3 disediakan dan array tidak kosong, maka metode pengurangan akan selalu memanggil fungsi callback mulai dari indeks 0

Jika const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); 3 tidak disediakan maka metode pengurangan akan bertindak berbeda untuk array dengan panjang lebih besar dari 1, sama dengan 1 dan 0, seperti yang ditunjukkan pada contoh berikut

const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError

Kode di bawah menunjukkan apa yang terjadi jika kita memanggil const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 5 dengan array dan tanpa nilai awal

const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); _

Panggilan balik akan dipanggil empat kali, dengan argumen dan nilai kembalian di setiap panggilan sebagai berikut

Parameter [15, 16, 17, 18, 19].reduce( (accumulator, currentValue) => accumulator + currentValue, 10, ); _4 tidak pernah berubah selama proses — selalu const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 05. Nilai yang dikembalikan oleh const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError _5 akan menjadi pemanggilan callback terakhir (const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 03)

Di sini kita mengurangi larik yang sama menggunakan algoritme yang sama, tetapi dengan const array = [15, 16, 17, 18, 19]; function reducer(accumulator, currentValue, index) { const returns = accumulator + currentValue; console.log( `accumulator: ${accumulator}, currentValue: ${currentValue}, index: ${index}, returns: ${returns}`, ); return returns; } array.reduce(reducer); 3 dari const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 09 diteruskan sebagai argumen kedua ke const getMax = (a, b) => Math.max(a, b); // callback is invoked for each element in the array starting at index 0 [1, 100].reduce(getMax, 50); // 100 [50].reduce(getMax, 10); // 50 // callback is invoked once for element at index 1 [1, 100].reduce(getMax); // 100 // callback is not invoked [50].reduce(getMax); // 50 [].reduce(getMax, 1); // 1 [].reduce(getMax); // TypeError 5

[15, 16, 17, 18, 19].reduce( (accumulator, currentValue) => accumulator + currentValue, 10, );

Panggilan balik akan dipanggil lima kali, dengan argumen dan nilai kembalian di setiap panggilan sebagai berikut