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## What is typing

**Typing** is the way a programming language manages **data types** (numbers, strings, objects, and so on).

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## Static vs Dynamic typing

| Characteristic | **Static typing** | **Dynamic typing** |
|---|---|---|
| When the type is determined | At **compile** time | At **run** time |
| Can the variable's type change | No | Yes |
| Example languages | TypeScript, Java, C#, C++ | JavaScript, Python, PHP |
| Type checking | Before the program runs | During execution |
| Error type on mismatch | Compilation error | Runtime error |

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## Example: JavaScript (dynamically typed)

```javascript
let value = 42;       // number
console.log(typeof value); // "number"

value = "Hello";      // now a string!
console.log(typeof value); // "string"

value = true;         // now a boolean value
console.log(typeof value); // "boolean"
```

Here, **the variable's type can change at runtime**,
and this is **normal** for JS.

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## Comparison example: TypeScript (statically typed)

```javascript
let value: number = 42;
value = "Hello"; // Error: type "string" is not assignable to type "number"
```

In TypeScript (or Java), the type is specified **once** and **cannot change**.

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## Consequences of dynamic typing

### Pros:

- Faster code writing, fewer "noisy" annotations.
- Flexibility: variables can be reused with different types.

### Cons:

- Errors only show up **at runtime**.
- Harder to debug large projects.
- Unexpected type conversions are possible:

```javascript
console.log('5' - 2); // 3   (string → number)
console.log('5' + 2); // "52" (number → string)
```

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## Summary

> JavaScript is a **dynamically and weakly typed language**,
> because:
>
> - the variable's type is determined **at runtime**,
> - and can **change at any moment**,
> - while the language **automatically converts types** when possible.

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