How do you use a variable in a regular expression?

How to Use a Variable in a Regular Expression 🧩🔤

Are you trying to create a String.replaceAll() method in JavaScript? 🤔 Do you want to use a regular expression to make it concise and efficient? 🚀 But wait... How do you pass a variable into a regular expression? 🤷‍♂️

Don't worry! In this blog post, we'll unravel the mystery and show you some easy solutions to this common issue. Let's dive in! 💪

The Challenge: Passing a Variable into a Regex String 🤔

Let's start by addressing the challenge at hand. You want to create a custom replaceAll() method in JavaScript. You have successfully used a regular expression to replace all instances of a particular character, like this:

"ABABAB".replace(/B/g, "A");

💡 Here, every occurrence of the character "B" is replaced with "A".

But now you want to take it a step further. You want to create a dynamic method that can replace any given character with a specific string. Your initial attempt looks like this:

String.prototype.replaceAll = function(replaceThis, withThis) {
    this.replace(/replaceThis/g, withThis);
};

Unfortunately, this approach doesn't work as expected. The regular expression /replaceThis/g treats "replaceThis" as a literal string and won't substitute it with the desired value. So how can you pass the variable into the regex string and make it work? 🧐

The Solution: Using the RegExp Constructor 🚀

To use a variable in a regular expression, you can leverage the RegExp constructor in JavaScript. This allows you to dynamically build your regular expression pattern using the variable's value. Let's modify your replaceAll() method to incorporate this technique:

String.prototype.replaceAll = function(replaceThis, withThis) {
    const regex = new RegExp(replaceThis, "g");
    return this.replace(regex, withThis);
};

🎉 And just like that, you can now pass variables into the regular expression! Let's see an example of this method in action:

const str = "ABABAB";
const replaceThis = "B";
const withThis = "A";

const result = str.replaceAll(replaceThis, withThis);
console.log(result); // Output: AAAAAA

Voila! By using the RegExp constructor, you successfully replace all occurrences of "B" with "A" in the string "ABABAB". 🎊

Your Turn: Level Up Your Regex Game! 💪

Now that you understand how to use a variable in a regular expression, it's time to level up your skills! 💥 Here's a challenge for you:

Try modifying the replaceAll() method to accept a case-insensitive flag. This way, you can replace occurrences regardless of the case sensitivity. Give it a shot! 👊

Once you've solved the challenge, share your solution in the comments below. We can't wait to see what you come up with! 🚀✨

Remember, practice makes perfect when it comes to regex. Keep exploring and experiment with different patterns to unlock the full potential of regular expressions. Happy coding! 😄👩‍💻👨‍💻

Cover image by Samuel Ramos on Unsplash