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How to test and execute a regular expression in JavaScript?
JavaScript provides two main methods for testing and executing regular expressions: test() and exec(). The test() method returns a boolean indicating if a pattern matches, while exec() returns detailed match information or null.
Regular Expression Methods
There are two primary ways to work with regular expressions in JavaScript:
- test() - Returns true/false if pattern matches
- exec() - Returns match details or null
Example: Using test() and exec()
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Regular Expression Testing</title>
<style>
body {
font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
padding: 20px;
}
.result, .sample {
font-size: 18px;
font-weight: 500;
margin: 10px 0;
}
.result {
color: green;
}
.btn {
background-color: #007bff;
color: white;
padding: 10px 20px;
border: none;
border-radius: 5px;
cursor: pointer;
}
</style>
</head>
<body>
<h1>Testing and Executing Regular Expressions</h1>
<div class="sample"></div>
<div class="result"></div>
<button class="btn">Test Regular Expression</button>
<h3>Click the button to test and execute the regular expression</h3>
<script>
let sampleEle = document.querySelector('.sample');
let resEle = document.querySelector('.result');
let str = 'Hello world. This is a beautiful world';
// Display the test string
sampleEle.innerHTML = 'Test String: ' + str;
// Create regular expression pattern
let pattern = new RegExp("world", "g");
document.querySelector(".btn").addEventListener("click", () => {
// Clear previous results
resEle.innerHTML = '';
// Reset regex lastIndex for global flag
pattern.lastIndex = 0;
// Test method - returns boolean
resEle.innerHTML += 'pattern.test(str) = ' + pattern.test(str) + '<br>';
// Reset for exec method
pattern.lastIndex = 0;
// Exec method - returns match details
let match = pattern.exec(str);
resEle.innerHTML += 'pattern.exec(str) = ' + match + '<br>';
resEle.innerHTML += 'Match found at index: ' + (match ? match.index : 'No match') + '<br>';
});
</script>
</body>
</html>
Understanding the Methods
test() Method
The test() method executes a search for a match between a regular expression and a string. It returns true if a match is found, false otherwise.
exec() Method
The exec() method executes a search for a match in a string. It returns an array with match information, or null if no match is found. The returned array contains:
- The matched text as the first element
- The index where the match was found
- The original input string
Output
When you run the code and click the button, you'll see:
Test String: Hello world. This is a beautiful world pattern.test(str) = true pattern.exec(str) = world Match found at index: 6
Key Differences
| Method | Return Type | Use Case |
|---|---|---|
test() |
Boolean | Check if pattern exists |
exec() |
Array or null | Get match details and position |
Conclusion
Use test() when you only need to verify if a pattern matches, and exec() when you need detailed information about the match, including its position and content.
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