JavaScript String indexOf() method

Using indexOf() with Strings

Here's an example of using indexOf() with strings:

let str = "Hello, world!";
let position = str.indexOf("world");
console.log(position); 

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In this case, indexOf() returns 7, which is the starting position of the substring "world" in str.

Using indexOf() with Arrays

The indexOf() method works similarly with arrays. Here's an example:
 

let arr = ["Apple", "Banana", "Mango", "Orange"];
let index = arr.indexOf("Mango");
console.log(index); 

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Here, indexOf() returns 2, which is the index of "Mango" in the array arr.

Case Sensitivity and Return Values

Remember that indexOf() is case-sensitive. It treats "a" and "A" as different characters. If indexOf() doesn't find the element, it returns -1.

JavaScript String indexOf() method examples

The indexOf() method in JavaScript is used to find the first occurrence of a substring within a given string. It returns the index of the first character of the first occurrence of the specified substring, or -1 if the substring is not found. Here are some examples of how to use the indexOf() method:

Basic Usage

• Javascript

Javascript

const text = "Hello, world!";
const position = text.indexOf("world");
console.log(position);

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Output 

7

Case-Sensitive Search

• Javascript

Javascript

const text = "Hello, World!";
const position = text.indexOf("world");
console.log(position); 

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Output

-1 (not found, case-sensitive)

Searching from a Specific Position

• Javascript

Javascript

const text = "This is a test. Is this test good?";
const position = text.indexOf("is", 5); // Start searching from index 5
console.log(position);

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Output

19

Checking for Non-existence

• Javascript

Javascript

const text = "Hello, world!";
const position = text.indexOf("universe");
console.log(position);

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Output

-1 (not found)

Finding All Occurrences

• Javascript

Javascript

const text = "This is a test. Is this test good?";
let position = text.indexOf("is");
while (position !== -1) {
  console.log(`Found "is" at index ${position}`);
  position = text.indexOf("is", position + 1);
}

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The indexOf() method is a useful tool for searching and manipulating strings in JavaScript. It's worth noting that there is also a related method called lastIndexOf(), which finds the last occurrence of a substring in a string.

Difference Between String indexOf() and String search()

Frequently Asked Questions

What is the use of indexOf in JavaScript?

In JavaScript, the indexOf method is used to determine the first index at which a given element can be found in an array or a substring in a string, returning -1 if not found.

What is the index in JavaScript?

In JavaScript, the index is the position of an element in an array or a character in a string, starting from 0.

What is the difference between indexOf and contains in JavaScript?

indexOf is a method that returns the index of the first occurrence of a value in a string or array, while includes (not "contains") returns a boolean indicating if a value is present.

Conclusion

In this article, we talked about the JavaScript String indexOf() method, which searches for a specified substring within a string and returns its index position. It is a simple but effective way to locate substrings and perform various string manipulation tasks in JavaScript.We also saw the difference between String indexOf() and String search().

To learn more about web development, we recommend reading the following articles:

• An Introduction to Javascript
• Resource Loading in JavaScript
• Object Oriented Programming In JavaScript.
   

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