Bugs encountered when using js variable scope

for (var i = 0; child && i <p>The above code creates a problem that seems very strange on the surface, that is, if kind! In the case of branch 2 of =4, sometimes the outer <a href="http://www.php.cn/code/9672.html" target="_blank">for loop</a> will turn back, that is: the outermost layer has obviously looped to the last child. After running branch 2, the outer for loop Go back and execute again. </p><p><strong>Cause analysis:</strong><br>I think if professionals are not as bad as me, they will find that the problem lies in <a href="http://www.php.cn/wiki/70.html" target="_blank">variable</a>i, where i will not become block level Variables, but <a href="http://www.php.cn/wiki/145.html" target="_blank">function</a>level. Changes in i in branch 2 will cause changes in outer i, causing the loop to return. <br>js did not have block-level scope before ES6, and was only divided into global scope and function-level scope. Here i is the function-level scope, and when we use it to do loops <a href="http://www.php.cn/code/9822.html" target="_blank">index</a>, in fact It is intended to be used as a block-level scope. </p><p><strong>Solution</strong></p><p>If you want to achieve the block-level scope effect, you can use the let keyword of ES6 syntax to achieve it: </p><pre class="brush:php;toolbar:false">for(let i=0;i<arr.length><p> I believe I read the case in this article You have mastered the method. For more exciting information, please pay attention to php Chinese website <a href="http://www.php.cn/java/java-alibaba-qita.html" target="_blank">Other</a> related articles! </p>
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