日付形式の検証中に JavaScript RegEx が機能しないのはなぜですか?

JavaScript RegEx Not Working

In a JavaScript code snippet, a regular expression (RegEx) is used to validate the format of a date string ("02/2010"). However, the RegEx test consistently returns false for all input values. Is there an issue with the code?

Answer:

Yes, the issue lies in the construction of the RegEx. When creating a RegEx from a string, it's crucial to double-up the backslashes ("\") to account for the parsing of the string as a JavaScript string constant.

The original RegEx:

var regEx = new RegExp("^(0[1-9]|1[0-2])/\d{4}$", "g");

becomes:

var regEx = new RegExp("^(0[1-9]|1[0-2])\\/\d{4}$", "g");

Alternatively, using RegEx syntax directly eliminates the need for double backslashes:

var regEx = /^(0[1-9]|1[0-2])\/\d{4}$/g;

Explanation:

The RegEx is split into three parts:

• Start of string: "^"

• Date format pattern: "(0[1-9]|1[0-2])\/\d{4}$"

  • Two digits (01-09 or 10-12) followed by a slash "/"
  • Four digits representing the year (\d{4})
• End of string: "$"

The backslashes ensure that the slashes and other characters within the pattern are recognized as part of the RegEx.

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