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JavaScript: Interpolation

In the lesson on concatenation, we solved the task of creating an email header out of two constants and punctuation marks. You probably solved it this way:

const firstName = 'Joffrey';
const greeting = 'Hello';

console.log(greeting + ', ' + firstName + '!');
// => 'Hello, Joffrey!'

It's a fairly simple task, but even here you should struggle to see what kind of string you end up with. You have to watch out for several quotation marks and spaces, and you can't tell where something starts and ends without paying attention.

There is a more convenient and elegant way to solve the same problem – interpolation. Here's what it looks like:

const firstName = 'Joffrey';
const greeting = 'Hello';

// Note that we are using backticks
// Interpolation won't work with single and double quotes
console.log(`${greeting}, ${firstName}!`);
// => 'Hello, Joffrey!'

We simply create a string and "insert" constants in proper places using the dollar sign and curly brackets ${ }. It's like we have a blank form where we can enter the desired values. And we no longer have to worry about separate strings for punctuation marks and spaces – all of these characters already exist in our template string.

You can create as many of these blocks as you want in a single string.

Interpolation only works with strings wrapped in backticks. This is the \` sign.

Nearly all languages favor interpolation over concatenation for combining strings. It glues a string together, and you see spaces and other characters inside it. Firstly, interpolation helps you to avoid confusing strings with numbers (thanks to the + sign), secondly, it is much easier (once you've practiced a little) to read a string as a whole.


Print the string Do you want to eat, <name>?, using the constant stark instead of <name>. The output should look like this:

Do you want to eat, Arya?
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 🙄

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  • Interpolation is a way to combine strings by embedding expressions in the template string using curly brackets. For instance, `Hi, ${name}!`.

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