# Week 1

Array methods are the Logic layer's core tools. Every backend request involves transforming data: filtering results, mapping to response formats, reducing to totals. These operations happen on nearly every request.

This week you'll learn the three essential methods: `forEach`, `map`, and `filter`. You'll understand when to use each one, and how they fit into the Data → Logic → Rendering model.

## Contents

* [Preparation](/course-content/backend/advanced-javascript/week1/preparation.md)
* [Slides](https://github.com/HackYourFuture-CPH/program/blob/main/courses/backend/advanced-javascript/week1/session-materials/slides/index.html)
* [Session Plan](/course-content/backend/advanced-javascript/week1/session-plan.md) (for mentors)
* [Session Materials](https://github.com/HackYourFuture-CPH/program/blob/main/courses/backend/advanced-javascript/week1/session-materials/README.md)
* [Assignment](/course-content/backend/advanced-javascript/week1/assignment.md)

## Learning Goals

By the end of this session, you will be able to:

* [ ] Use `forEach` for side effects (logging, rendering)
* [ ] Use `map` to transform arrays (N items → N transformed items)
* [ ] Use `filter` to select items (N items → fewer items, same shape)
* [ ] Combine multiple array methods through chaining
* [ ] Use arrow function syntax with implicit and explicit returns
* [ ] Recognize which methods belong in the Logic layer vs Rendering layer
* [ ] Know how to find and learn about other array methods such as `.find()`, `.some()`, `.reduce()`

### After this session you will understand code like this

```js
// Example: Get names of organic Japanese teas
const result = teas
  .filter((tea) => tea.origin === "Japan")
  .filter((tea) => tea.organic)
  .map((tea) => tea.name);
// ["Sencha", "Matcha"]
```


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