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JavaScript: Standard library

Like any other language, JavaScript comes with a set of useful functions. All together they make up the so-called standard library. It usually contains thousands of functions you can't remember, and you don't have to. It is assumed that any programmer knows where to look for their documentation and has a rough idea of what they want to achieve. And the rest is a matter of technique. Without the Internet, most programmers wouldn't be able to program anything.

To newcomers, it often looks like this: "Go I know not whither and fetch I know not what". In other words, most people have no idea how to learn about these functions when they don't know anything at all. Oddly enough, there is no way to know everything you need to know once and for all. As you grow as a developer, you learn all the exciting features that solve your problems more elegantly, thus expanding your toolbox.

Here are some tips to learn about new features:

  • Always keep track of what you are working with (the data type) at the moment. You will most likely find the function you need in the appropriate chapter of the documentation. For example, you need to study string functions to work with strings
  • From time to time, open the standard functions section of the topic you are studying and just run through them, learning the signatures and ways to use them
  • Read other people's code more often, especially code from the libraries you're using. It's all available on GitHub

The JavaScript standard library's structure has its peculiarities. Since the code can run in different environments, such as a server or a browser, the capabilities of the standard library are highly dependent on the use case. For example, you can't perform some server tasks in a browser. For server-side documentation, see The server portions of the standard library are organized into modules, each module has its own page with full descriptions of all its functions. In particular, the module fs is required to work with the file system, its functions allow you to write and read files.

As for the browsers, there's not much stuff. For the most part, it's some basic functions built into the language. For example, the math functions we've seen before.. The rest of the features you can add via third-party libraries.


The typeof operator defines the type of the operand. The type name returns as a string. For example, calling typeof 'go go go' will return the string 'string'.

console.log(typeof 3); // => 'number'

Print the type of the value of the constant motto.

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.



  • Standard library is a set of useful features bundled in the programming language.

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