Javascript 这是什么代码？/^(\d{4}|\d{6})$/

What code is this? /^(\d{4}|\d{6})$/

提问by Tucker Beauchamp

So I am extremely new to the Javascript world. I was practicing on codewars having to analyze a pin to make sure it only contained numbers and was either 4 or 6 characters. I looked at the most clever code and the answer was:

所以我对 Javascript 世界非常陌生。我正在练习代码战，必须分析一个 pin 以确保它只包含数字并且是 4 或 6 个字符。我看了最聪明的代码，答案是：

function validatePIN(pin) {
  return /^(\d{4}|\d{6})$/.test(pin)
}

I've never seen the "/^(\d{4}|\d{6})$/" bit before. Could anyone tell me what this is called so I can research it on my own, or give me a breakdown of how it works?

我以前从未见过 "/^(\d{4}|\d{6})$/" 位。谁能告诉我这叫什么，这样我就可以自己研究它，或者给我详细说明它是如何工作的？

回答by Draco18s no longer trusts SE

It's a regular expression.

这是一个正则表达式。

I tend to use http://www.regexpal.com/when I want to try and find the expression I need, there's also http://regexr.com/for learning about them (among other resources).

当我想尝试找到我需要的表达式时，我倾向于使用http://www.regexpal.com/，还有http://regexr.com/用于了解它们（以及其他资源）。

回答by STW

It's a regular expression literal, similar to using return new RegExp('^(\\d{4}|\\d{6})$').test(pin)The "literal" part implies that it's a means of representing a specific data type as a string in code—just like trueand 'true'are different, as one is a boolean literal and the other is a string literal.

它是一个正则表达式字面量，类似于使用return new RegExp('^(\\d{4}|\\d{6})$').test(pin)“字面量”部分意味着它是一种将特定数据类型表示为代码中的字符串的方法——就像true和'true'不同，一个是布尔字面量，另一个是字符串字面量.

Specifically, the regex ^(\d{4}|\d{6})$breaks down to:

具体来说，正则表达式^(\d{4}|\d{6})$分解为：

^       a string that starts with...
(       either
  \d    a digit (0-9)...
  {4}   that repeats four times...
|       or
  \d    a digit (0-9)...
  {6}   that repeats six times...
)
$       and then ends

So: '1234', '123456', etc would match. '123.00', '12345','abc123',' 1234', ' 1234 'would not match.

所以: '1234', '123456', 等会匹配。'123.00', '12345', 'abc123', ' 1234',' 1234 '不匹配。

As noted by several others in the comments on Draco18s' answerthere are several nuances to be aware of with using regex literals in JS:

正如其他几个人在对Draco18s 回答的评论中所指出的，在 JS 中使用正则表达式文字时需要注意几个细微差别：

• The literal syntax doesn't require you to escape special characters within the regex pattern. Using the RegExp constructor requires you to represent the pattern as a string, which in turn requires escaping. Note the differences of the \'s between the two syntaxes.

• Using a regex literal will treat the regex as a constant, whereas using new RegExp()leaves life cycle management of the regex instance up to you.

  The literal notation is compiled and implies a constant regex, whereas the constructor version is reparsed from the string, and so the literal is better optimized/cached. jsperf.com/regexp-literal-vs-constructor/4Note: you can get basically the same effect by caching the new Regex in a variable, but the literal one is cached at the JIT step – user120242

  In other words, using a regex literal can avoid potential performance pitfalls:

  Example:

  for (var i = 0; i < 1000; i++) {
    // Instantiates 1x Regex per iteration
    var constructed = new RegExp('^(\d{4}|\d{6})$') 
  
    // Instantiates 1 Regex
    var literal = /^(\d{4}|\d{6})$/ 
  }
  

• 文字语法不需要您在正则表达式模式中转义特殊字符。使用 RegExp 构造函数要求您将模式表示为字符串，而这又需要转义。请注意\'s 在两种语法之间的差异。

• 使用正则表达式文字会将正则表达式视为常量，而使用new RegExp()正则表达式实例的生命周期管理由您决定。

  文字符号被编译并暗示一个常量正则表达式，而构造函数版本是从字符串中重新解析的，因此文字被更好地优化/缓存。jsperf.com/regexp-literal-vs-constructor/4注意：通过将新的 Regex 缓存在一个变量中可以获得基本相同的效果，但字面值是在 JIT 步骤缓存的 – user120242

  换句话说，使用正则表达式可以避免潜在的性能缺陷：

  例子：

  for (var i = 0; i < 1000; i++) {
    // Instantiates 1x Regex per iteration
    var constructed = new RegExp('^(\d{4}|\d{6})$') 
  
    // Instantiates 1 Regex
    var literal = /^(\d{4}|\d{6})$/ 
  }
  

回答by user120242

Good reference for Javascript RegExp
http://www.regular-expressions.info/javascript.html

Javascript RegExp 的良好参考
http://www.regular-expressions.info/javascript.html

^ beginning of line
\d = all digits
{4} = repetition 4 times
| = "or"
$ end of line

your example tests for a 4 digit string or 6 digit string

您的示例测试 4 位字符串或 6 位字符串