Passing Variable To A Regexp In Javascript Duplicate

When coding in JavaScript, knowing how to pass variables to a regular expression (regex) can be a handy skill to have. In this guide, we will walk you through the process of passing a variable to a regex in JavaScript.

Regular expressions are powerful tools for pattern matching and finding specific parts of a string. When you need to use a regex pattern multiple times with different variables, it's more efficient to pass these variables dynamically.

Here's how you can pass a variable to a regex in JavaScript:

1. Creating a Regex Object: First, you need to create a regex object using the `RegExp` constructor. This allows you to define the regex pattern as a string and include variables in it.

let searchTerm = "example"; // Variable to search for
let regexPattern = new RegExp(searchTerm, "i"); // 'i' flag for case-insensitive search

In this example, we're creating a regex pattern that will search for the value of the `searchTerm` variable in a case-insensitive manner.

2. Using the Regex Object: Now that you have your regex object, you can use it to match against strings.

let text = "This is an example text for demonstration.";
if (regexPattern.test(text)) {
    console.log("Match found!");
} else {
    console.log("No match found!");
}

In the above code block, we're testing if the regex pattern matches the `text` string. The `test` method returns `true` if there is a match and `false` otherwise.

3. Extracting Matches: You can also extract the matched parts of the string using the `exec` method.

let match = regexPattern.exec(text);
if (match) {
    console.log("Matched text: " + match[0]);
} else {
    console.log("No match found!");
}

The `exec` method returns an array containing the matched text along with any captured groups.

4. Dynamic Regex Patterns: You can construct dynamic regex patterns using variables.

let dynamicSearchTerm = "dynamic";
let dynamicRegexPattern = new RegExp(dynamicSearchTerm, "i");

By creating regex patterns dynamically, you can easily change the search criteria without hard-coding the pattern.

In conclusion, passing a variable to a regex in JavaScript is a useful technique for flexible and efficient pattern matching. By following these steps and examples, you can harness the power of regular expressions in your JavaScript code effectively. Happy coding!