How to Find Substring in JavaScript: Simple Methods Explained

In JavaScript, you can find a substring using the includes() method to check if it exists, or indexOf() to get its position. Both methods work on strings and help you locate parts of text easily.

Syntax

The two main methods to find a substring in JavaScript are includes() and indexOf().

• string.includes(substring): Returns true if substring is found, otherwise false.
• string.indexOf(substring): Returns the starting index of substring if found, otherwise -1.

javascript

let text = "Hello, world!";

// Check if 'world' is in text
let hasWorld = text.includes("world");

// Find position of 'world'
let position = text.indexOf("world");

Example

This example shows how to check if a substring exists and find its position in a string.

javascript

const sentence = "I love learning JavaScript!";

// Check if 'JavaScript' is in the sentence
const containsJS = sentence.includes("JavaScript");
console.log(containsJS); // true

// Find the starting index of 'learning'
const indexLearning = sentence.indexOf("learning");
console.log(indexLearning); // 7

// Try to find a substring that does not exist
const indexPython = sentence.indexOf("Python");
console.log(indexPython); // -1

Output

true
7
-1

Common Pitfalls

One common mistake is expecting indexOf() to return true or false instead of a number. Remember, it returns -1 if the substring is not found.

Also, includes() is case-sensitive, so "Hello" and "hello" are different.

javascript

const text = "Hello World";

// Wrong: expecting boolean from indexOf
if (text.indexOf("world") !== -1) {
  console.log("Found it!");
} else {
  console.log("Not found.");
}

// Right way
if (text.indexOf("world") !== -1) {
  console.log("Found it!");
} else {
  console.log("Not found.");
}

// Case sensitivity example
console.log(text.includes("world")); // false
console.log(text.includes("World")); // true

Output

Found it!
Not found.
false
true

Quick Reference

Method	Description	Return Value	Case Sensitive
includes(substring)	Checks if substring exists	true or false	Yes
indexOf(substring)	Finds starting index of substring	Index number or -1	Yes

Key Takeaways

Use includes() to check if a substring exists, returning true or false.

Use indexOf() to find the position of a substring; it returns -1 if not found.

Both methods are case-sensitive, so watch your letter cases.

Remember indexOf() returns a number, not a boolean.

For simple substring checks, includes() is more readable and direct.