JavaScript Fundamentals · Arrays · Lesson 16 of 48
Creating and Accessing Arrays
Concept
Creating and Accessing Arrays
Arrays store ordered lists of values, accessed by a zero-based index.
Because indexing starts at 0, the last item in an array sits at index length - 1, not at index length — a classic off-by-one spot to double check.
By the end of this lesson
- Explain the core idea behind Creating and Accessing Arrays.
- Predict output before running a change.
- Test one realistic and one unusual input.
- Use the result to make the next decision.
How to study this page
- 1. Read one concept.
- 2. Change the example.
- 3. Run, compare, and explain.
- 4. Complete the challenge below.
Syntax
const arrayName = [item1, item2, item3];
arrayName[index]ExampleRunnable
const colors = ["red", "green", "blue"];
console.log(colors[0], colors.length);Accessing the last item safely
const colors = ["red", "green", "blue"];
console.log(colors[colors.length - 1]);Note: colors.length - 1 always points to the last element, no matter how long the array is.
Self-check before continuing
Without looking at the example, describe what changes when you modify one input in Creating and Accessing Arrays. Then reopen the editor and prove your explanation with a small test.
You are ready to continue when you can predict, test, and explain the result.
Your turn
Create an array of 5 numbers and log the last one using its index.
Loading editor…
Console