JavaScript Concepts Step by Step

Interactive step-by-step explanations of JavaScript concepts. Click on a concept to explore examples.

Functions

Create different types of functions and understand function scope and callbacks.

7 examples

Booleans & Conditions

Understand true/false values and how they help code make decisions.

4 examples

Strings

Work with text, indexing, interpolation, and common string methods.

8 examples

Objects

Store related data with key/value pairs - properties. Learn property access, dynamic keys, looping over properties, and destructuring.

6 examples

For Loops

Learn how different types of for loops work with iteration, arrays, and strings.

6 examples

Arrays

Learn the core ideas: ordered lists, indexing, length, mutation vs non-mutation, and copying vs shared references.

5 examples

Array Map

Transform arrays by applying a function to each element. Explore explicit returns, implicit returns, and practical use cases.

4 examples

Array Filter

Create new arrays containing only elements that pass a test. Learn to filter by conditions, clean data, and combine criteria.

5 examples

Array forEach

Execute a function for each array element. Learn side effects, working with objects, and how it compares to for..of.

5 examples

Array Reduce

Reduce arrays to a single value using accumulator patterns with and without initial values.

2 examples