How to Check if String Matches Pattern in JavaScript

In JavaScript, you can check if a string matches a pattern using the RegExp.test() method or the string method match(). Both use regular expressions to define the pattern you want to check against.

Syntax

Use the RegExp.test() method to check if a string matches a pattern. It returns true if the pattern is found, otherwise false.

Syntax:

• pattern.test(string) - Returns true or false.
• string.match(pattern) - Returns an array of matches or null if no match.

javascript

const pattern = /yourPattern/;
const string = "your string here";

const result = pattern.test(string); // true or false
const matches = string.match(pattern); // array or null

Example

This example checks if the string contains only digits using a regular expression. It shows how to use test() and match() methods.

javascript

const pattern = /^\d+$/; // pattern for digits only
const string1 = "12345";
const string2 = "123abc";

console.log(pattern.test(string1)); // true
console.log(pattern.test(string2)); // false

console.log(string1.match(pattern)); // [ '12345', index: 0, input: '12345', groups: undefined ]
console.log(string2.match(pattern)); // null

Output

true
false
[ '12345', index: 0, input: '12345', groups: undefined ]
null

Common Pitfalls

Common mistakes include:

• Not using the correct regular expression delimiters /pattern/.
• Forgetting to escape special characters in the pattern.
• Using match() expecting a boolean instead of an array or null.
• Confusing test() and match() return types.

Example of wrong and right usage:

javascript

// Wrong: expecting boolean from match()
const pattern = /abc/;
const string = "abcdef";
const resultWrong = string.match(pattern) === true; // false, match returns array or null

// Right: use test() for boolean
const resultRight = pattern.test(string); // true

console.log(resultWrong); // false
console.log(resultRight); // true

Output

false
true

Quick Reference

Method	Description	Return Type
RegExp.test(string)	Checks if pattern matches string	Boolean (true/false)
string.match(pattern)	Finds matches of pattern in string	Array of matches or null
RegExp.exec(string)	Executes a search for a match	Array with match details or null

Key Takeaways

Use RegExp.test() to get a simple true or false if a string matches a pattern.

Use string.match() to get detailed match results or null if no match.

Always write regular expressions between slashes, like /pattern/.

Escape special characters in patterns to avoid errors.

Remember test() returns boolean, match() returns array or null.