JavaScript lesson 4: Numbers and operators
US version. US grades and US spelling. · UK version of this lesson
JavaScript does math with + - * and /. Division gives the exact answer: 7 / 2 is 3.5 – there is no separate whole-number division. A complete 40-minute JavaScript lesson for beginners (Grades 7–8), from Unit 2: Variables and numbers. It runs right here in your browser – nothing to install.
- Time
- 40 minutes + 20 min homework
- Grade
- Grades 7–8 (ages 12–13)
- You need
- A computer or tablet, paper and a pencil
- Graded
- 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 – graded 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: Where in real life would you use the remainder, %?
Watch out for
7 / 2is 3. Run it: / gives 3.5. Use Math.floor for whole numbers.2 + 3 * 4is 20. Multiplication first: 2 + 12 is 14.
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
Learning goal: use + - * / and % and **.
Success looks like
- I can use
+ - * /and%and**. - I can use the order of operations.
- I can round with
Math.floor()andMath.round().
Key words
operator · remainder · order of operations · Math.floor · decimal
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)
JavaScript does math with + - * and /. Division gives the exact answer: 7 / 2 is 3.5 – there is no separate whole-number division.
% gives the remainder (7 % 3 is 1) and ** means "to the power of" (2 ** 3 is 8). Brackets come first, then **, then * / %, then + -.
Math.floor(x) rounds down and Math.round(x) rounds to the nearest whole number. Computers store decimals in binary, so 0.1 + 0.2 shows 0.30000000000000004 – use toFixed(2) to show 2 decimal places.
Worked example – see it
console.log(12 / 8)
It prints:
1.5
The lesson, step by step
| Part | Time | How it is checked |
|---|---|---|
| Starter | 5 min | Graded by Classfern |
| Teaching input | 8 min | Read, watch and talk |
| See it, then predict | 8 min | Graded by Classfern |
| Put it in order, write it, fix it | 14 min | Graded by Classfern |
| Closure and exit ticket | 5 min | Graded 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 graded instantly.
Practice tests
Curriculum
CSTA K–12 Computer Science Standards (2017), grades 6–8: 2-AP-11 – Create clearly named variables of different data types and operate on them.
The standard codes are CSTA's; the descriptions are our own words.
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.