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## Definition

> **String concatenation** is an operation in which **two or more strings are joined into one**.

---

## Example

```javascript
const firstName = 'Oleh';
const lastName = 'Kovalenko';

const fullName = firstName + ' ' + lastName;

console.log(fullName); // "Oleh Kovalenko"
```

Here the `+` operator is used to **glue strings together**.
JS does not add them as numbers, it joins them, because at least one operand is a string.

---

## Behavior of the `+` operator

If one of the operands is a string,
JS **automatically converts** the other operand to a string:

```javascript
'Age: ' + 25;  // "Age: 25"
'Answer: ' + true;  // "Answer: true"
'Array: ' + [1,2,3]; // "Array: 1,2,3"
```

> This is an example of **implicit type coercion**.

---

## Example with multiple strings

```javascript
const message = 'Hello, ' + 'world' + '!';
console.log(message); // "Hello, world!"
```

---

## Alternative: template literals

The modern approach (ES6+) is to use **backticks** `` ` ``
and **embed variables via** `${}`:

```javascript
const name = 'Oleh';
const age = 25;

const message = `My name is ${name}, I am ${age} years old.`;

console.log(message); // "My name is Oleh, I am 25 years old."
```

> This is also **concatenation**, but more readable and more powerful.
> It lets you easily add variables, line breaks and expressions.

---

## Example with line breaks

Before (pre-ES6):

```javascript
const text = 'First line\n' + 'Second line';
```

With template literals:

```javascript
const text = `
First line
Second line
`;
```

---

## Concatenation of different types

```javascript
console.log('5' + 5);   // "55"
console.log('true: ' + true); // "true: true"
console.log(1 + '2' + 3); // "123"
```

> JS **always turns numbers into strings**,
> if at least one operand is a string.

---

## Summary

| Method | Example | Result |
|---|---|---|
| The `+` operator | `'Hello ' + 'World'` | `'Hello World'` |
| Template literals | `Hello ${name}` | `'Hello Oleh'` |
| Implicit conversion | `'Age: ' + 25` | `'Age: 25'` |

---

## In short

> Concatenation = joining strings together.
> Done through `+` or template literals `...${}...`.
> If at least one operand is a string, JS converts everything to a string.

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