How to Use test() Method in JavaScript Regex

In JavaScript, use the test() method on a regular expression object to check if a pattern exists in a string. It returns true if the pattern matches and false otherwise.

Syntax

The test() method is called on a regular expression object and takes a string as input. It returns a boolean indicating if the pattern matches anywhere in the string.

• regex: The regular expression object.
• string: The text to test against the regex.
• Returns true if the pattern is found, otherwise false.

javascript

regex.test(string)

Example

This example shows how to check if the word "hello" exists in a string using test(). It prints true if found, otherwise false.

javascript

const regex = /hello/;
const text1 = "hello world";
const text2 = "goodbye world";

console.log(regex.test(text1)); // true
console.log(regex.test(text2)); // false

Output

true
false

Common Pitfalls

One common mistake is using the test() method with a global /g flag on the regex. This causes test() to remember the last index and can give unexpected results on repeated calls.

Always avoid the /g flag when using test() or reset the regex lastIndex manually.

javascript

const regex = /hello/g;
const text = "hello hello";

console.log(regex.test(text)); // true
console.log(regex.test(text)); // false (unexpected)

// Correct way without /g flag
const regex2 = /hello/;
console.log(regex2.test(text)); // true
console.log(regex2.test(text)); // true

Output

true
false
true
true

Quick Reference

Usage	Description
regex.test(string)	Returns true if regex matches string, else false
/pattern/.test(text)	Checks if 'pattern' exists in 'text'
Avoid /g flag with test()	Global flag causes stateful behavior and bugs
Returns boolean	Use in if conditions or logical checks

Key Takeaways

Use regex.test(string) to check if a pattern exists in a string and get a true/false result.

Do not use the global /g flag with test() to avoid unexpected false results on repeated calls.

test() returns a boolean and is useful for simple pattern presence checks.

Call test() directly on a regex object with the string you want to check.

Remember test() only tells if a match exists, not what or where it is.