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
• Slides
• Session Plan (for mentors)
• Session Materials
• Assignment

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

// 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"]