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JavaScript: Arithmetic operations

At the most basic level, computers only use numbers. Even in high-level language applications, there are many numbers and operations with them. To get started with programming all you need to know is basic arithmetic – let’s start with that.

When adding two numbers in math, we write, for example, 3 + 4. The same goes for programming. Here is a program that adds two numbers:

// Don't forget the semicolon at the end,
// since each line of code is a statement

3 + 4;

The statement 3 + 4 makes the computer add up the numbers and find the result. If you run this program, nothing will happen. Well, the computer will calculate the sum, of course, but that'll be it. The result of the sum isn't used, and as such, this program has no real value. We need to ask the computer to add 3 + 4, and then give it a command to do something with the result. For example, print it:

// The sum is calculated first,
// it is then passed to the print function

console.log(3 + 4);

After launching, the result will appear on the screen:


Besides addition, the following operations are available:
* — multiplication
/ — division
- — subtraction
%modulo (remainder after division)
** — power

Now let's print the result of division, and then the result of exponentiation:

console.log(8 / 2);  // => 4
console.log(3 ** 2); // => 9

Sometimes we will show the result of the executed code in the comments like this: => RESULT. For example, // => 4.

The first statement will print 4 (since 8 / 2 is 4), and the second statement will print 9 (since 32 is 9).


Print the result of dividing 81 by 9.

The exercise doesn't pass checking. What to do? 😶

If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:

  • Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.

I've read the lessons but nothing is clear 🙄

It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.

By the way, you can participate in courses improvement. There is a link below to the lessons course code which you can edit right in your browser.


  • Always indent arithmetic operators with spaces between the numbers (operands) - it is good form when programming. This is why we write console.log(3 + 4), and not console.log(3+4) in our examples.

  • The result of dividing by zero is Infinity. We will figure out what this means in later lessons.

  • Arithmetic operators

If you got stuck and don't know what to do, you can ask a question in our community