How to Convert User Input Strings to Regular Expressions in a Regular Expression Tester?

Converting User Input String to Regular Expression

When developing a regular expression tester, it's crucial to handle user-entered regular expressions correctly. The challenge lies in accepting user input as a string while ensuring it can be converted into a regular expression object. There are several approaches to addressing this issue:

Using RegExp Constructor with Delimiters:

The RegExp object constructor allows you to create a regular expression from a string. To include delimiters (//) in the user-entered string, you can use the constructor in the following format:

var re = new RegExp("/a|b/i");
// Equivalent to
var re = /a|b/i;

Parsing String and Flags:

If you don't want users to enter delimiters, you can manually parse the input string. Identify the regular expression pattern and the flags (if any) by split the string at the last / character:

const userString = "a|b/i";
const pattern = userString.substring(0, userString.lastIndexOf("/"));
const flags = userString.substring(userString.lastIndexOf("/") + 1);

const re = new RegExp(pattern, flags);

Separate Flags:

Alternatively, you can ask users to enter the regular expression pattern and flags separately. This approach provides more control over flag handling, as users can specify multiple flags or leave them blank.

By implementing one of these methods, you can convert user-entered strings into regular expression objects, ensuring that your regex tester can handle user input effectively.

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