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JavaScript: What is a variable

Consider this task: we need to print the phrase Father! two times or even five times. You can solve it via brute force:


This will do for the most basic case, but if you use the phrase Father! more often and in different parts of your code, you have to repeat it everywhere. Then you will face even more issues when it turns out that you need to change the phrase. This is a common scenario in development. We have to find all the occurrences of the phrase Father! and make all the required changes. There is one other way to do it. Instead of copying our expression, just create a variable containing this phrase.

let greeting = 'Father!';
console.log(greeting); // => Father!
console.log(greeting); // => Father!

A variable points to data that it stores. It allows you to use the data multiple times without duplicating it. The variable is created and filled with data (initialized) using the statement let greeting = 'Father!'.

The variable name can consist of characters from any valid character set including English letters and numbers as well as _ and $ signs. Note that you can't place a digit at the beginning of a name. Variable names are case-sensitive, which means that hello and heLLo are two different names and thus two distinct variables. Case is really important in JavaScript, so never forget it.

You don't have to initialize the variable with data when declaring it. Sometimes you may want to create a variable and fill it later:

let greeting;

// Usage
console.log(greeting); // undefined

// We'll learn about changing a variable in the next lesson

A declared but uninitialized variable contains an undefined value. This is a special value used when nothing is defined.

You can create any number of variables. Large programs contain dozens or hundreds of thousands of variable names:

let greeting1 = 'Father!';

let greeting2 = 'Mother!';

For the sake of the code analysis, it's common to create variables near the place they are used.


Create a variable with the name motto containing What Is Dead May Never Die!. Print its contents.

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.



  • Variable is a way to save data under a name for later use in code.

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