循环：For 循环、While 循环、ForOf 循环、ForIn 循环

for (let i = 1; i 



<p>要循环数组，我们可以执行以下操作：<br></p>

<pre class="brush:php;toolbar:false">const animals = ['lizard', 'fish', 'turtle'];

for (let i = 0; i 



<p>我们还可以反向循环这个数组：<br></p>

<pre class="brush:php;toolbar:false">for (let i = animals.length - 1; i &gt;= 0; i--) {
  console.log(i, animals[i]);
}

// 2 'turtle'
// 1 'fish'
// 0 'lizard'

for (let i = 0; i 



<p>如果我们想要迭代数组的数组，这很有用：<br></p>

<pre class="brush:php;toolbar:false">const seatingchart = [
  ['abigale', 'tim', 'cynthia'],
  ['bob', 'carter', 'zane', 'tanja'],
  ['quin', 'xavier'],
];

// to print each name individually from seatingchart:
for (let i = 0; i 



<h2>
  
  
  while 循环
</h2>

<p>简单 while 循环的一个例子是：<br></p>

<pre class="brush:php;toolbar:false">let num = 0;

// to print out 0 through 4:
while (num 



<h2>
  
  
  中断关键字
</h2>

<p>break关键字可用于退出while循环：<br></p>

<pre class="brush:php;toolbar:false">let input = prompt('say something:');
while (true) {
  input = prompt(input);
  if (input === 'stop copying me') {
    break; // finally stops prompting user
  }
}

let line = ['abby', 'salvia', 'jamie', 'carter', 'john'];

for (let i = 0; i 



<h2>
  
  
  for...of 循环
</h2>

<p>如果我们想打印数组中的每个值，我们可以这样做：<br></p>

<pre class="brush:php;toolbar:false">let people = ['agitha', 'bruce', 'charlie', 'dane', 'ernie'];
// to print each persons name:
for (let person of people) {
  console.log(person);
}

const seatingchart = [
  ['abigale', 'tim', 'cynthia'],
  ['bob', 'carter', 'zane', 'tanja'],
  ['quin', 'xavier'],
];

// to print each name individually from seatingchart:
for (let row of seatingchart) {
  for (let person of row) {
    console.log(person);
  }
}

const testscores = {
  jim: 34,
  abby: 93,
  greg: 84,
  mark: 95,
  melvin: 73,
};

for (let person in testscores) {
  console.log(`${person} scored ${testscores[person]}`);
}

let total = 0;
let scores = Object.values(testScores);
for (let score of scores) {
  total += score;
}
let avg = total / scores.length;
console.log(avg);