Learn JavaScript: Arrays and Iteration
Create arrays to store your information and learn how to iterate over these collections.
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Key Concepts
Review core concepts you need to learn to master this subject
Property .length
Property .length
const numbers = [1, 2, 3, 4];
numbers.length // 4The .length property of a JavaScript array indicates the number of elements the array contains.
Arrays
Lesson 1 of 4
- 2One way we can create an array is to use an array literal. An array literal creates an array by wrapping items in square brackets []. Remember from the previous exercise, arrays can store any da…
- 3Each element in an array has a numbered position known as its index. We can access individual items using their index, which is similar to referencing an item in a list based on the item’s positi…
- 4In the previous exercise, you learned how to access elements inside an array or a string by using an index. Once you have access to an element in an array, you can update its value. let seasons =…
- 5You may recall that you can declare variables with both the let and const keywords. Variables declared with let c…
- 6One of an array’s built-in properties is length and it returns the number of items in the array. We access the [.length](https://www.codecademy.com/resources/docs/javascript/strings/length?page_ref…
- 7Let’s learn about some built-in JavaScript methods that make working with arrays easier. These methods are specifically called on arrays to make common tasks, like adding and removing elements, mor…
- 8Another array method, .pop(), removes the last item of an array. const newItemTracker = [‘item 0’, ‘item 1’, ‘i…
- 9There are many more array methods than just .push() and .pop(). You can read about these array methods on the Docs entry for [JavaScript Arrays](https://www.codecademy.com/resources/docs/javascript…
- 10Throughout the lesson we went over arrays being mutable, or changeable. Well what happens if we try to change an array inside a function? Does the array keep the change after the function call or i…
- 11Earlier we mentioned that arrays can store other arrays. When an array contains another array it is known as a nested array. Examine the example below: const nestedArr = [[1], [2, 3]]; To acce…
- 12Nice work! In this lesson, we learned these concepts regarding arrays: * Arrays are lists that store data in JavaScript. * Arrays are created with brackets []. * Each item inside of an array is a…
What you'll create
Portfolio projects that showcase your new skills
How you'll master it
Stress-test your knowledge with quizzes that help commit syntax to memory