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JavaScript: Simplified function syntax

Compared to some (primarily functional) languages, function definition in JavaScript looks rather cumbersome:

const square = (x) => {
  return x ** 2;

It uses a lot of extra characters and the word return. Since version ES6, an alternative, shorter syntax has appeared in the language, making it much easier to understand and shorten code in some cases.

// It takes a little time to get used to it,
// but after a while it'll save your life
const double = (x) => x ** 2;

There are two differences from the full definition, it omits the curly brackets and the return statement. The shortened version carries out the return automatically. It means that there is exactly one computable expression inside such a function, and its result will be immediately returned.

Note that the differences are purely syntactic, there are no differences in terms of usage. An example with two arguments:

The full version

const sum = (a, b) => {
  return a + b;

The shortened version

const sum = (a, b) => a + b;

Note the absence of curly brackets. Developers unaccustomed to this syntax sometimes write const sum = (a, b) => { a + b }; and then have a hard time understanding why it doesn't work. The answer is simple: if there are curly brackets, then this isn't the shortened form, which means if you want the function to return a value, you will have to use return.


Write the capitalize() function that takes a non-empty string and converts the first letter of the first word to uppercase:

const name = 'arya';
console.log(capitalize(name)); // => "Arya"

To get a substring (or character) from a string, use the slice() method:

'welcome'.slice(2, 5); // "lco"

To convert the string to uppercase, use the toUpperCase() method:

'welcome'.toUpperCase(); // "WELCOME"
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.

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