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String search

Learn to search with .indexOf, .includes and .startsWith.

Searching with indexOf

To find a substring's position you use the .indexOf() method. "hello world".indexOf("world") returns 6 because "world" starts at index 6. Indexing is zero-based.

If the substring is not found .indexOf() returns -1. This value is often used to check whether a substring exists: if (text.indexOf("@") !== -1) roughly tests whether a text might be an email.

includes and startsWith

.includes() returns true/false for whether a substring exists in a string: "welcome".includes("come") evaluates to true. It is a more readable form of .indexOf() !== -1.

.startsWith() tests whether a string begins with the given substring: "Mr. Smith".startsWith("Mr.") is true. Its counterpart .endsWith() checks the end. All three methods are case-sensitive.

Practice Find and print the index

The sentence variable holds "Node.js rocks". Declare a variable pos and assign the result of sentence.indexOf("rocks") to it. Then print pos with console.log. The output on a single line must be 8.

Starter code

index.js
const sentence = "Node.js rocks";
// Declare pos with indexOf and print it

Sample solution

index.js
const sentence = "Node.js rocks";
const pos = sentence.indexOf("rocks");
console.log(pos);

Expected output

8

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Match each method to its job

Term Meaning
.indexOf(x) Returns first index
.includes(x) Asks whether it exists
.startsWith(x) Checks the start
.length Character count

2 What is the result of "notebook".includes("book")?

index.js
"notebook".includes("book")
  • false
  • -1
  • 4
  • true Correct answer

Explanation: "book" is in "notebook"; includes returns true.

3 Write the startsWith call

Question 
const code = "US-CA";
const ok = code____("US-");
Answer 
const code = "US-CA";
const ok = code.startsWith("US-");

Explanation: .startsWith checks the start of the string.

All lessons in Beginner

1 Node.js basics

  1. What is Node.js?
  2. Your first program
  3. ES modules
  4. package.json
  5. CommonJS vs ESM
  6. Summary - Node.js basics

2 Variables

  1. let and const
  2. var and scope
  3. Type inference
  4. Destructuring
  5. Spread and rest
  6. Summary - Variables

3 Data types

  1. Primitive types
  2. Template literals
  3. Number and Math
  4. Symbol
  5. typeof
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. process.argv
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Nullish coalescing
  6. Summary - Operators

6 Strings

  1. String methods
  2. String search
  3. substring and slice
  4. replace and split
  5. padStart and trim
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. switch
  4. Ternary
  5. Optional chaining
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. for...of
  4. for...in
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. push and pop
  4. shift and unshift
  5. splice and slice
  6. Summary - Arrays

11 Array methods

  1. map
  2. filter
  3. reduce
  4. find and some
  5. forEach
  6. Summary - Array methods

12 Objects

  1. Object literal
  2. Property access
  3. Computed properties
  4. Object methods
  5. Object spread
  6. Summary - Objects

13 Functions

  1. Defining functions
  2. Return values
  3. Arrow functions
  4. Default parameters
  5. Rest parameters
  6. Summary - Functions

14 Callbacks

  1. What are callbacks?
  2. Higher-order functions
  3. forEach with callbacks
  4. Error-first callbacks
  5. Callback hell
  6. Summary - Callbacks

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Promises

  1. What are promises?
  2. then and catch
  3. Promise.all
  4. Promise.race
  5. finally
  6. Summary - Promises

17 async/await

  1. async function
  2. await
  3. try/catch
  4. await with Promise.all
  5. Sequential await
  6. Summary - async/await

18 fs module

  1. fs.promises
  2. readFile
  3. writeFile
  4. appendFile
  5. existsSync
  6. Summary - fs module

19 path module

  1. path.join
  2. path.resolve
  3. path.parse
  4. path.dirname and basename
  5. path.extname
  6. Summary - path module

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. fs persistence
  5. Putting it together