Cara menggunakan praktik terbaik perulangan javascript

Question

Loop menawarkan cara cepat dan mudah untuk melakukan sesuatu berulang kali. Bab Panduan JavaScript ini memperkenalkan berbagai pernyataan iterasi yang tersedia untuk JavaScript

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Anda dapat menganggap loop sebagai versi permainan yang terkomputerisasi di mana Anda memberi tahu seseorang untuk mengambil X langkah ke satu arah, lalu Y melangkah ke arah lain. Misalnya, gagasan "Pergi lima langkah ke timur" dapat diekspresikan dengan cara ini sebagai satu putaran

for (let step = 0; step < 5; step++) {
  // Runs 5 times, with values of step 0 through 4.
  console.log('Walking east one step');
}

Ada banyak jenis loop, tetapi semuanya pada dasarnya melakukan hal yang sama. mereka mengulangi tindakan beberapa kali. (Perhatikan bahwa ada kemungkinan angka itu bisa nol. )

Berbagai mekanisme loop menawarkan cara yang berbeda untuk menentukan titik awal dan akhir dari loop. Ada berbagai situasi yang lebih mudah dilayani oleh satu jenis loop daripada yang lain

Pernyataan untuk loop yang disediakan dalam JavaScript adalah

Sebuah

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

_3 loop berulang sampai kondisi tertentu bernilai false. Loop JavaScript

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

_3 mirip dengan loop Java dan C

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

3

Pernyataan

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

_3 terlihat sebagai berikut

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

Saat

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

3 loop dijalankan, hal berikut terjadi

Ekspresi inisialisasi

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

8, jika ada, dijalankan. Ekspresi ini biasanya menginisialisasi satu atau lebih penghitung loop, tetapi sintaks memungkinkan ekspresi tingkat kerumitan apa pun. Ekspresi ini juga dapat mendeklarasikan variabel

Ekspresi

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

9 dievaluasi. Jika nilai

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

_9 benar, pernyataan loop akan dieksekusi. Jika tidak, loop

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

_3 berakhir. (Jika ekspresi

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

9 dihilangkan seluruhnya, kondisi dianggap benar. )

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

_3 dijalankan. Untuk mengeksekusi banyak pernyataan, gunakan pernyataan blok (

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

4) untuk mengelompokkan pernyataan tersebut

Jika ada, ekspresi pembaruan

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

5 dijalankan

Kontrol kembali ke Langkah 2

Pada contoh di bawah, fungsi berisi pernyataan

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

3 yang menghitung jumlah opsi yang dipilih dalam daftar gulir (elemen

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

7 yang memungkinkan beberapa pilihan)

HTML

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

_

JavaScript

Di sini, pernyataan

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

_3 mendeklarasikan variabel

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

9 dan menginisialisasi ke

do
  statement
while (condition);

0. Ini memeriksa bahwa

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

_9 kurang dari jumlah opsi dalam elemen

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

7, melakukan pernyataan

do
  statement
while (condition);

3 berikutnya, dan menambah

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

9 dengan 1 setelah setiap melewati loop

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

Pernyataan

do
  statement
while (condition);

_5 berulang hingga kondisi tertentu bernilai salah

Pernyataan

do
  statement
while (condition);

_5 terlihat sebagai berikut

do
  statement
while (condition);

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

3 selalu dieksekusi sekali sebelum kondisi diperiksa. (Untuk mengeksekusi banyak pernyataan, gunakan pernyataan blok (

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

4) untuk mengelompokkan pernyataan tersebut. )

Jika

do
  statement
while (condition);

_9 adalah

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

0, pernyataan dijalankan lagi. Di akhir setiap eksekusi, kondisi diperiksa. Ketika kondisinya adalah

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

1, eksekusi berhenti, dan kontrol diteruskan ke pernyataan berikut

do
  statement
while (condition);

5

Dalam contoh berikut, loop

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

_3 berulang setidaknya sekali dan berulang hingga

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

9 tidak lagi kurang dari

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

5

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

Pernyataan

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

_6 mengeksekusi pernyataannya selama kondisi tertentu bernilai

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

0. Pernyataan

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

_6 terlihat sebagai berikut

while (condition)
  statement

Jika

do
  statement
while (condition);

_9 menjadi

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

1,

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

3 dalam loop berhenti mengeksekusi dan kontrol beralih ke pernyataan setelah loop

Tes kondisi terjadi sebelum

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

_3 dalam loop dijalankan. Jika kondisi mengembalikan

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

0,

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

3 dieksekusi dan

do
  statement
while (condition);

9 diuji lagi. Jika kondisi mengembalikan

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

1, eksekusi berhenti, dan kontrol diteruskan ke pernyataan berikut

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

6

Untuk mengeksekusi banyak pernyataan, gunakan pernyataan blok (

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

4) untuk mengelompokkan pernyataan tersebut

Loop

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

6 berikut berulang selama

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

0 kurang dari

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

1

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

Dengan setiap iterasi, loop bertambah

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

0 dan menambahkan nilai itu ke

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

3. Oleh karena itu,

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

3 dan

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

0 mengambil nilai-nilai berikut

Setelah lulus pertama.

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

0 =

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

7 dan

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

3 =

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

7

Setelah lulus kedua.

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

0 =

// Infinite loops are bad!
while (true) {
  console.log('Hello, world!');
}

1 dan

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

3 =

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

1

Setelah lulus ketiga.

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

0 =

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

1 dan

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

3 =

// Infinite loops are bad!
while (true) {
  console.log('Hello, world!');
}

7

Setelah menyelesaikan lintasan ketiga, kondisi

// Infinite loops are bad!
while (true) {
  console.log('Hello, world!');
}

8 tidak lagi

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

0, sehingga perulangan berakhir

Hindari loop tak terbatas. Pastikan kondisi dalam sebuah loop pada akhirnya menjadi

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

1—jika tidak, loop tidak akan pernah berakhir. Pernyataan dalam

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

_6 loop berikut dijalankan selamanya karena kondisinya tidak pernah menjadi

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

1

// Infinite loops are bad!
while (true) {
  console.log('Hello, world!');
}

label:
  statement

_3 memberikan pernyataan dengan pengidentifikasi yang memungkinkan Anda merujuk ke tempat lain di program Anda. Misalnya, Anda dapat menggunakan label untuk mengidentifikasi sebuah loop, dan kemudian menggunakan pernyataan

label:
  statement

4 atau

label:
  statement

5 untuk menunjukkan apakah suatu program harus menghentikan loop atau melanjutkan eksekusinya

Sintaks pernyataan berlabel terlihat seperti berikut

label:
  statement

Nilai dari

label:
  statement

3 dapat berupa pengidentifikasi JavaScript apa pun yang bukan merupakan kata khusus.

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

_3 yang Anda identifikasi dengan label dapat berupa pernyataan apa pun

Dalam contoh ini, label

label:
  statement

_8 mengidentifikasi loop

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

6

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

0

Gunakan pernyataan

label:
  statement

_4 untuk mengakhiri loop,

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

01, atau bersamaan dengan pernyataan berlabel

Ketika Anda menggunakan

label:
  statement

4 tanpa label, itu menghentikan penutup terdalam

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

6,

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

04,

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

3, atau

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

01 segera dan mentransfer kendali ke pernyataan berikut

Saat Anda menggunakan
```
label:
  statement
```
4 dengan label, ini mengakhiri pernyataan berlabel yang ditentukan

Sintaks pernyataan

label:
  statement

_4 terlihat seperti ini

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

1

Bentuk pertama dari sintaks mengakhiri loop terlampir terdalam atau

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

01

Bentuk kedua dari sintaks mengakhiri pernyataan berlabel terlampir yang ditentukan

Contoh berikut mengulangi elemen dalam array hingga menemukan indeks elemen yang nilainya

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

10

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

2

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

_3

Pernyataan

label:
  statement

_5 dapat digunakan untuk memulai kembali pernyataan

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

6,

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

04,

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

3, atau

label:
  statement

3

Saat Anda menggunakan

label:
  statement

5 tanpa label, ini menghentikan iterasi saat ini dari pernyataan terlampir terdalam

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

6,

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

04, atau

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

3 dan melanjutkan eksekusi loop dengan iterasi berikutnya. Berbeda dengan pernyataan

label:
  statement

_4,

label:
  statement

5 tidak menghentikan eksekusi loop seluruhnya. Dalam

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

6 loop, itu melompat kembali ke kondisi. Dalam

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

_3 loop, itu melompat ke

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

24

Saat Anda menggunakan
```
label:
  statement
```
_5 dengan label, ini berlaku untuk pernyataan perulangan yang diidentifikasi dengan label tersebut

Sintaks pernyataan

label:
  statement

_5 terlihat seperti berikut

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

_4

Contoh berikut menunjukkan

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

_6 loop dengan pernyataan

label:
  statement

5 yang dijalankan ketika nilai

function countSelected(selectObject) {
  let numberSelected = 0;
  for (let i = 0; i < selectObject.options.length; i++) {
    if (selectObject.options[i].selected) {
      numberSelected++;
    }
  }
  return numberSelected;
}

const btn = document.getElementById('btn');

btn.addEventListener('click', () => {
  const musicTypes = document.selectForm.musicTypes;
  console.log(`You have selected ${countSelected(musicTypes)} option(s).`);
});

9 adalah

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

1. Jadi,

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

_0 mengambil nilai-nilai

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

7,

let n = 0;
let x = 0;
while (n < 3) {
  n++;
  x += n;
}

1,

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

34, dan

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

35

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

5

Jika Anda mengomentari

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

_36, perulangan akan berjalan hingga akhir dan Anda akan melihat

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

37

Pernyataan berlabel

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

_38 berisi pernyataan berlabel

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

39. Jika

label:
  statement

_5 ditemui, program menghentikan iterasi saat ini dari

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

39 dan memulai iterasi berikutnya. Setiap kali

label:
  statement

5 ditemui,

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

39 mengulang sampai kondisinya kembali

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

1. Ketika

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

1 dikembalikan, sisa pernyataan

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

38 selesai, dan

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

38 mengulang sampai kondisinya kembali

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

1. Ketika

let i = 0;
do {
  i += 1;
  console.log(i);
} while (i < 5);

1 dikembalikan, program berlanjut pada pernyataan berikut

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

38

Jika

label:
  statement

_5 memiliki label

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

38, program akan berlanjut di bagian atas pernyataan

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

38

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

_6

Pernyataan

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

_54 mengulangi variabel yang ditentukan atas semua properti enumerable dari suatu objek. Untuk setiap properti yang berbeda, JavaScript mengeksekusi pernyataan yang ditentukan. Pernyataan

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

54 terlihat sebagai berikut

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

_7

Fungsi berikut menggunakan objek dan nama objek sebagai argumennya. Itu kemudian mengulangi semua properti objek dan mengembalikan string yang mencantumkan nama properti dan nilainya

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

_8

Untuk objek

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

_56 dengan properti

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

57 dan

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

58,

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

59 akan menjadi

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

_9

Meskipun mungkin tergoda untuk menggunakan ini sebagai cara untuk mengulangi

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

60 elemen, pernyataan

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

54 akan mengembalikan nama properti yang ditentukan pengguna selain indeks numerik

Oleh karena itu, lebih baik menggunakan loop

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

_3 tradisional dengan indeks numerik saat melakukan iterasi pada array, karena pernyataan

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

54 melakukan iterasi pada properti yang ditentukan pengguna selain elemen array, jika Anda memodifikasi objek Array (seperti menambahkan properti khusus atau metode)

Pernyataan

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

_64 membuat loop Iterasi pada objek yang dapat diubah (termasuk objek

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

60,

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

66,

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

67,

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

68, dan seterusnya), memohon pengait iterasi khusus dengan pernyataan yang akan dieksekusi untuk nilai setiap properti yang berbeda

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

_0

Contoh berikut menunjukkan perbedaan antara

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

_64 loop dan

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

54 loop. Sementara

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

_54 mengulangi nama properti,

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

64 mengulangi nilai properti

<form name="selectForm">
  <label for="musicTypes">Choose some music types, then click the button below:</label>
  <select id="musicTypes" name="musicTypes" multiple>
    <option selected>R&B</option>
    <option>Jazz</option>
    <option>Blues</option>
    <option>New Age</option>
    <option>Classical</option>
    <option>Opera</option>
  </select>
  <button id="btn" type="button">How many are selected?</button>
</form>

_1

Pernyataan

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

_64 dan

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

54 juga dapat digunakan dengan destrukturisasi. Misalnya, Anda dapat mengulang kunci dan nilai objek secara bersamaan menggunakan

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

75

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