js loop traversal

The content of this article is about loop traversal in js. Now I share it with everyone, and it can also be used as a reference for friends in need

Method 1

<span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);"><br>    var </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">arr </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">= </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">[</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">1</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">2</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">3</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">4</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">5</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">];<br></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">    for</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">let </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">i </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">= </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">0</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">;<span style="margin:0px;padding:0px;">i</span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);"><</span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">arr</span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">.length;<span style="margin:0px;padding:0px;">i</span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">++</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">){<br/>        </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);">//...<br/></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">    }</span>

# The disadvantage of method 1 using a for loop to traverse the array is that the code is not enough concise.

## The following is a more concise way of writing.

Method 2

<span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);"><br/>    var </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">arr </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">= </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">[</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">1</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">2</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">3</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">4</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">5</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">];<br/><span style="margin:0px;padding:0px;">    arr</span>.</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(166,226,46);">forEach</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">function </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(</span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(253,151,31);">value</span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(253,151,31);">index</span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">) {<br/>       </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);">//...<br/></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">    });<br/>    <br/></span>

# This uses the Foreach loop code to be much less. The writing is more concise. The disadvantage is that the entire cycle cannot be stopped.

#Method 3

<span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);"><br/>    var </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">arr </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">= </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">[</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">1</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">2</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">3</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">4</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">5</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">];<br/></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">    for</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">let </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">i </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">in </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">arr</span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">){<br/>        </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);">//...<br/></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">    }<br/>    <br/></span>

for...in循环更常用于对象的循环，如果用于数组的循环，那么就要注意了，上述代码中每次循环中得到的i是字符串类型，而不是预料中的数字类型，要想对它进行运算，那得先要进行类型转换，造成不方便。

来看看for...of的是实现：

<span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);"><br/>    var </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">arr </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">= </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">[</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">1</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">2</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">3</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">4</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">5</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">];<br/></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">    for</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">let </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">value </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">of <span style="margin:0px;padding:0px;">arr</span>){<br/>        <span style="margin:0px;padding:0px;">console</span>.</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(166,226,46);">log</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(<span style="margin:0px;padding:0px;">value</span>);<br/>    }<br/></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);">    //</span><span style="margin:0px;padding:0px;font-size:18px;color:rgb(117,113,94);">打印结果：依次输出：</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);">1 2 3 4 5<br/><br/></span>

看样子是不是有点眼熟，很像for...in？确实很像。它的实现跟for...in很类似。

我们列举一下for...of的优势：

1. 写法比for循环简洁很多；

2. 可以用break来终止整个循环，或者continute来跳出当前循环，继续后面的循环；

3. 结合keys( )获取到循环的索引，并且是数字类型，而不是字符串类型。

   
   

分别来展示一下上述的几个优点：

循环可以终止

<span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);"><br/>    var </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">arr </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">= </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">[</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">1</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">2</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">3</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">4</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">5</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">];<br/></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">    for</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">let </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">value </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">of <span style="margin:0px;padding:0px;">arr</span>){<br/>        </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">if</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(<span style="margin:0px;padding:0px;">value </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">== </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">3</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">){<br/>            </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);">//</span><span style="margin:0px;padding:0px;font-size:18px;color:rgb(117,113,94);">终止整个循环<br/></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">            break</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">;<br/>        }<br/>        <span style="margin:0px;padding:0px;">console</span>.</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(166,226,46);">log</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(<span style="margin:0px;padding:0px;">value</span>);<br/>    }<br/></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);">    //</span><span style="margin:0px;padding:0px;font-size:18px;color:rgb(117,113,94);">打印结果：</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);">1 2<br/><br/></span>

以上案例：用break实现了终止整个循环，不会继续后面的遍历，所以打印结果为：1 2。

可跳过当前循环

<span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);"><br/>    var </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">arr </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">= </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">[</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">1</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">2</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">3</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">4</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">5</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">];<br/></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">    for</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">let </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">value </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">of <span style="margin:0px;padding:0px;">arr</span>){<br/>        </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">if</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(<span style="margin:0px;padding:0px;">value </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">== </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">3</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">){<br/>            </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);">//</span><span style="margin:0px;padding:0px;font-size:18px;color:rgb(117,113,94);">跳过当前循环，继续后面的循环<br/></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">            continue</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">;<br/>        }<br/>        <span style="margin:0px;padding:0px;">console</span>.</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(166,226,46);">log</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(<span style="margin:0px;padding:0px;">value</span>);<br/>    }<br/></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);">    //</span><span style="margin:0px;padding:0px;font-size:18px;color:rgb(117,113,94);">打印结果：</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);">1 2 4  5<br/><br/></span>

用continue跳过当前循环，继续后面的循环，所以打印结果为：1 2 4 5。

得到数字类型的索引

<span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);"><br/>    var </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">arr </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">= </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">[</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">1</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">2</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">3</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">4</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">,</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(174,129,255);">5</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">];<br/></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">    for</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">let </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">index </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">of <span style="margin:0px;padding:0px;">arr</span>.</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(166,226,46);">keys</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">()){<br/>        <span style="margin:0px;padding:0px;">console</span>.</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(166,226,46);">log</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(<span style="margin:0px;padding:0px;">index</span>);<br/>    }<br/></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);">    //</span><span style="margin:0px;padding:0px;font-size:18px;color:rgb(117,113,94);">打印结果：依次输出</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);">:0 1 2 3 4<br/><br/></span>

使用数组的扩展keys( )（第八节有介绍，点击查看），获取键名再遍历，得到的index是数字类型的。

此外，相比于for...in循环专门为对象设计，for...of循环的适用范围更广。

遍历字符串

for...of 支持字符串的遍历。

<span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);"><br/>    let </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">word </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">= </span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(230,219,116);">"</span><span style="margin:0px;padding:0px;font-size:18px;color:rgb(230,219,116);">我是前端小菜鸟</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(230,219,116);">"</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">;<br/></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">    for</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">let </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">w </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">of <span style="margin:0px;padding:0px;">word</span>){<br/>        <span style="margin:0px;padding:0px;">console</span>.</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(166,226,46);">log</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(<span style="margin:0px;padding:0px;">w</span>);<br/>    }<br/></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);">    //</span><span style="margin:0px;padding:0px;font-size:18px;color:rgb(117,113,94);">打印结果：我  是  前  端  小  菜  鸟<br/><br/></span>

遍历DOM List

for...of支持类数组的遍历，例如DOM List。

<span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);"><br/>    <</span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(227,227,255);">p</span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">><span style="margin:0px;padding:0px;">1</span></</span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(227,227,255);">p</span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">><br>    <</span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(227,227,255);">p</span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">><span style="margin:0px;padding:0px;">2</span></</span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(227,227,255);">p</span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">><br>    <</span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(227,227,255);">p</span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">><span style="margin:0px;padding:0px;">3</span></</span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(227,227,255);">p</span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">><br></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);">    //</span><span style="margin:0px;padding:0px;color:rgb(117,113,94);">假设有<span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;">3</span>个<span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;">p</span>元素</span><span style="margin:0px;padding:0px;"><br></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">    let </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">pList </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">= </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">document</span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">.</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(166,226,46);">getElementsByTagName</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(230,219,116);">'p'</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">);<br><br></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">    for</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(249,38,114);">let </span><span style="margin:0px;padding:0px;"><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">p </span></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">of <span style="margin:0px;padding:0px;">pList</span>){<br>        <span style="margin:0px;padding:0px;">console</span>.</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(166,226,46);">log</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(248,248,242);">(<span style="margin:0px;padding:0px;">p</span>);<br></span><span style="margin:0px;padding:0px;color:rgb(248,248,242);font-family:Consolas;font-size:18px;line-height:1.6;">    }<br></span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);">    // </span><span style="margin:0px;padding:0px;color:rgb(117,113,94);">打印结果：</span><span style="margin:0px;padding:0px;font-size:18px;font-family:Consolas;color:rgb(117,113,94);"><p>1</p><br></span><span style="margin:0px;padding:0px;color:rgb(117,113,94);font-family:Consolas;font-size:18px;line-height:1.6;">    //          <p>2</p><br>    //          <p>3</p></span>

       还有一些其它的遍历 后续再添加~···

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