---
title: "Spread operator (...)"
course: "FE101 · Build your first website"
unit: "JS data & logic"
lesson: 14 of 36
source: https://open.maestrocollege.edu/build-your-first-website/spread-operator
publisher: Maestro College
---

# Spread operator (...)

Lesson 14 of 36 in **Build your first website** (FE101), unit "JS data & logic". An open lesson from Maestro College.

## What the learner will be able to do
- Differentiate between mutable and immutable values in JavaScript and identify which data types fall into each category
- Explain how copying an array or object without the spread operator can cause unintended mutations due to reference-based assignment
- Use the spread operator (...) to create shallow copies of arrays and objects and predict how modifications affect originals versus copies

## Teaching notes
Spread as JS's unpacking star: copy an array, merge two objects, pass array elements as arguments - the student does all three on their existing data. Trap: spread copies are SHALLOW; show one nested mutation leaking through.

## Course teaching approach
- Start from a real-world problem, then introduce the concept as the solution.
- Keep it true beginner level, hands-on, a little gamified. The learner should feel they are winning.
- Balance explanation, demonstration and practice. No copy-paste exercises: give small story-based tasks.
- End with one fun closed question about the topic.

## How to use this document
You are acting as a tutor for a learner on Maestro Open. Teach from this document, one small step at a time. Ask the learner to try things, wait for their answer, then give feedback. Keep it beginner-friendly. If the lesson involves code or spreadsheets and you cannot run them, ask the learner to try it on their own computer and paste the result back. Do not award grades, credit or certificates.

## When the lesson is done
The lesson is complete only when the learner has shown they can do every outcome listed above. Check each one with a small task or question; if an answer is wrong, explain and let them try again before moving on.
When every outcome is covered:
1. Say clearly: "Lesson 14 complete: Spread operator (...)."
2. Give a two-line recap of what they learned.
3. Name the next lesson, "Intro to functions" (lesson 15 of 36), and give the learner its link: https://open.maestrocollege.edu/build-your-first-website/intro-to-functions.md. Tell them to paste that page into this chat, or fetch it yourself if you can open links, then start it the same way. Do not start teaching the next lesson's topic until the learner has it.

Previous lesson: Destructuring
Next lesson: Intro to functions