Скачать или смотреть Getting the String Length of a Regular Expression Capture Group in JavaScript

Learn how to dynamically replace a password in a URL with asterisks based on its length using JavaScript's regular expressions.
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This video is based on the question https://stackoverflow.com/q/64707944/ asked by the user 'Justin' ( https://stackoverflow.com/u/425964/ ) and on the answer https://stackoverflow.com/a/64707958/ provided by the user 'CertainPerformance' ( https://stackoverflow.com/u/9515207/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem

In JavaScript, working with regular expressions is a common task, whether you're validating input or manipulating strings. One interesting situation arises when you want to mask sensitive information, such as passwords, in a URL.

For instance, if you have a MongoDB connection string and you need to replace the actual password with asterisks, it can be tricky if you want the number of asterisks to match the length of the password, rather than a fixed number.

The Challenge

You have a connection string like:

[[See Video to Reveal this Text or Code Snippet]]

Where "bar" is the password and you want to replace it with asterisks ('*****'), but you need it to match the actual length of the password.

Here's the regular expression you're working with:

[[See Video to Reveal this Text or Code Snippet]]

This code snippet, however, just hardcodes the replacement with five asterisks, which won't work for passwords of varying lengths. So, how do you dynamically adjust the number of asterisks based on the password length?

The Solution: Using a Callback Function

The key to solving this problem lies in using a callback function within the replace method. Here's how you can achieve it step by step:

Step 1: Define the URL

Start off by defining your connection string:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Create a Censor Function

Next, create a function that will replace each character in the password with an asterisk. This can be done using string replacement or a repeat function:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Use the Replace Method with a Callback

Now, incorporate the censor function into your replace method by using a callback to capture the different parts of the URL:

[[See Video to Reveal this Text or Code Snippet]]

In this code:

g1, g2, and g3 correspond to the matched groups from the regular expression.

g2 is the password, which you pass to the censor function to get the appropriate number of asterisks.

Step 4: Output the Result

Finally, log the redacted URL to the console:

[[See Video to Reveal this Text or Code Snippet]]

Example Output

If the original URL was mongodb://foo:bar@ baz, after running the above code, the output would be:

[[See Video to Reveal this Text or Code Snippet]]

Where *** corresponds to the length of bar.

Conclusion

By using a callback function combined with regular expressions, you can effectively mask sensitive information in a string dynamically based on its actual length. This technique ensures that your data remains secure, even when handling variable-length strings such as passwords.

Now you can confidently replace passwords in your connection strings, keeping them safe and hidden behind the appropriate number of asterisks!