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Session Plan (Week 1: Array Methods)

This guide is for mentors. It outlines how to run the session, what to emphasize, and why we introduce certain terminology.

Session Goals

By the end of this session, trainees should:

  1. Understand when to use forEach, map, and filter
  2. Be able to chain array methods together
  3. Write arrow functions with implicit and explicit returns
  4. Connect array methods to the Data → Logic → Rendering model

Glossary Goals

Term Why we introduce it
Declarative vs Imperative Frames the shift from for-loops to array methods. Helps them understand why this style is preferred.
Higher-order function They'll encounter this term in docs, tutorials, and interviews. Demystifies "functions that take functions."
Side effect Critical for understanding forEach vs other methods. Foundation for async concepts in Week 2.
Predicate Precise term for filter functions. Common in documentation and libraries.
Pipeline Mental model for chaining. Useful metaphor they'll use throughout their career.

Session Outline

1. Introduction

  • Connect to the course theme: Data → Logic → Rendering
  • Array methods live in the Logic layer - transforming data between storage and display
  • Show the tea shop context they'll work with

Use: Slides (first few sections)

2. forEach

  • Start with function() syntax, NOT arrow functions
  • Emphasize: no return value - it's for side effects
  • Live code example: logging tea names

Key point: "If you need to do something for each item but don't need a result back, use forEach."

Exercises: Part 1 (exercises 1-3)

3. map

  • Still using function() syntax
  • Emphasize: same count in, same count out
  • Contrast with forEach: map returns a new array, forEach doesn't
  • Live code: extract tea names, calculate prices

Key point: "If you need to transform each item into something else, use map."

Exercises: Part 2 (exercises 4-6)

4. filter

  • Introduce the term predicate - a function returning true/false
  • Emphasize: items stay the same shape, count changes
  • Live code: organic teas, Japanese teas

Key point: "If you need to select some items based on a condition, use filter."

Exercises: Part 3 (exercises 7-10)

5. Combining methods

  • Introduce pipeline metaphor
  • Show chaining: filter → map
  • Discuss order: usually filter first (reduce data), then map (transform)

Exercises: Part 4 (exercises 11-13)

6. Arrow functions

  • NOW introduce arrow syntax
  • Show the progression: function() → arrow → implicit return
  • Practice converting earlier exercises

Key point: "Arrow functions are shorter syntax for the same thing. They're popular because they reduce noise in array methods."

Exercises: Part 5 (exercises 14-16)

7. Wrap-up

  • Recap the three methods and when to use each
  • Show the "questions to ask" slide
  • Introduce the assignment

Teaching Tips

Managing exercises with mixed skill levels

The exercises are intentionally numerous - trainees progress at different speeds. Here's how to manage this:

  1. Let trainees work on Part 1 - observe how far each gets individually
  2. Solve one exercise in plenum - pick one that weaker trainees struggled with but stronger trainees just finished. This way everyone benefits
  3. Move on to Part 2 - weaker trainees skip remaining Part 1 exercises (they can revisit later)
  4. Repeat for each part

Exercises marked with ⭐ are optional stretch goals. If your fastest trainees finish all exercises while others haven't solved the first one, that part needs an additional challenge - let us know, or create a PR with a creative challenging exercise!

Use the tea data consistently

All examples should use the tea shop data. This builds familiarity and shows how the same dataset can be queried different ways.

Connect to backend context

Regularly remind them: "This is what happens on every API request. Data comes in one shape, goes out another."

Materials

  • Slides - Reveal.js presentation
  • Exercises - In-session exercises
  • Assignment - Take-home work
  • Tea Data - Shared dataset that you can find in your assignment repo