Regular expressions are the ace up the sleeve of many of the most talented programmers out there. With a solid understanding of how regular expressions work, it’s sometimes possible to bypass a tangled mess of conditional logic and recursive function calls with a simple one-liner that just gets the job done much more efficiently.

正则表达式是许多最有才华的程序员的王牌。 有了对正则表达式的工作原理的深刻理解，有时可以使用简单的单行代码绕开缠结的条件逻辑和递归函数调用，从而更有效地完成工作。

One of the convenient places to use regular expressions is when doing form validation. With HTML5 it’s possible to enforce attributes like field length, but if someone tries to mess with your security and post values without using the form, you need to be able to verify that what you intended and what you’re getting are consistent.

使用正则表达式的便利位置之一是进行表单验证时。 使用HTML5，可以强制执行诸如字段长度之类的属性，但是如果有人试图破坏您的安全性并在不使用表单的情况下发布值，则需要能够验证您的意图和所获得的内容是否一致。

To check the length of a string,