JavaScript lesson 20: Objects and properties
UK version. UK school years and UK spelling. · US version of this lesson
An object keeps related values together under names: const pet = { name: "Rex", age: 3 }. Each name is a property. A complete 40-minute JavaScript lesson for beginners (Year 8, KS3), from Unit 8: Objects. It runs right here in your browser – nothing to install.
- Time
- 40 minutes + 20 min homework
- Year
- Year 8, KS3 (ages 12–13)
- You need
- A computer or tablet, paper and a pencil
- Marked
- Instantly, with explanations
For parents: how to use this lesson
You don't need to know JavaScript yourself. The lesson explains each step on screen, the way Mr Babbage, our Head of Computing, likes it: a worked example first, then a go for your child. Code questions run your child's program in the browser – marked straight away.
- Read what your child will learn together.
- Press Start the lesson below. Sit with your child for the teaching and the worked example (about 16 minutes): ask them to say what each line does.
- Let them do the practice on their own. When code goes wrong, the error message is a clue – let them read it out and try again before you help.
- Finish with the talk question: Describe yourself as an object: what properties would you have?
Watch out for
- A missing property is an error. It is undefined – until you use undefined the wrong way.
pet.keyuses the variable key. Use pet[key].
Miss Lovelace's tip for home: ask your child to explain one line of their program to you in their own words. If they can explain it, they understand it – and every error message is a clue, not a failure.
What your child will learn
We are learning to store named values in an object.
Success looks like
- I can store named values in an object.
- I can read and change properties with
.and[ ]. - I can explain what
undefinedmeans for a property.
Key words
object · property · key · value · undefined
What to have ready
- A device with a web browser (the code runs in the browser – nothing to install)
- Paper for tracing
- A keyboard helps for typing code (a tablet or phone works too)
The big ideas (for the adult)
An object keeps related values together under names: const pet = { name: "Rex", age: 3 }. Each name is a property.
pet.name reads a property and pet.age = 4 changes it. A property that isn't there gives undefined – so a misspelt property name gives undefined, not an error.
When the property name is in a variable, use brackets: pet[key]. pet.key would look for a property literally called "key". Object.keys(pet) lists the names.
Worked example – see it
const player = { name: "Ava", score: 2 }
console.log(player["score"])It prints:
2
The lesson, step by step
| Part | Time | How it is checked |
|---|---|---|
| Starter | 5 min | Marked by Classfern |
| Teaching input | 8 min | Read, watch and talk |
| See it, then predict | 8 min | Marked by Classfern |
| Put it in order, write it, fix it | 14 min | Marked by Classfern |
| Plenary and exit ticket | 5 min | Marked by Classfern + self-check |
The lesson
It runs here on the page. No sign-up and no names – progress is kept only in this browser. Each visit picks a new mix of questions.
Homework
20 minutes: 7 questions – predict what code prints, write or fix a short program, and check the key ideas – then a short reflection. New questions every time, all marked instantly.
Practice tests
Curriculum
National curriculum in England, computing, key stage 3: pupils should be taught to use 2 or more programming languages, at least one of which is textual, to solve a variety of computational problems; make appropriate use of data structures [for example, lists, tables or arrays]; design and develop modular programs that use procedures or functions; and to design, use and evaluate computational abstractions that model the state and behaviour of real-world problems and physical systems.
Contains public sector information licensed under the Open Government Licence v3.0.
Our lessons and questions are our own. They are not written or endorsed by any government department, testing agency or exam board. JavaScript is a trademark or registered trademark of Oracle Corporation in the U.S. and other countries; Classfern is not affiliated with or endorsed by it.