Python to JavaScript Translation Guide
### Definitions
- **Statement**: A single instruction in JavaScript.
- **Sequence**: Linear sequence of statements, same as in Python.
- **Control**: Conditional execution using `if`.
- **Loop**: Repeating statements using `for` or `while`.
- **Function**: Block of code defined using `function`.
- **Recursion**: Function that calls itself.
### Data Types and Variables
- **Literal**: Fixed values like `1`, `true`, `"hello"`.
- **Variable**: Assigned via `=` (e.g., `let x = 10;`).
- **Global variable**: Available in global scope.
### Operators
- **Arithmetic operators**: `+`, `-`, `*`, `/`, `%`, `**`
- **Logic operators**: `&&`, `||`, `!`
- **Comparison operators**: `==`, `===`, `!=`, `!==`, `>`, `<`, `>=`, `<=`
### Control Structures
- **If-Else**: `if`, `else if`, `else`
- **Loops**: `for`, `while`, `do...while`, `break`, `continue`
- **Try-Catch**: Exception handling with `try`, `catch`, `finally`
- **Function Definitions**: Using `function` keyword or arrow functions `() => {}`
### Control of Data
- **Mutable vs Immutable**: Objects and arrays are mutable; primitives like numbers and strings are immut
- **Namespaces**: JavaScript uses scope to manage variable access.
### Iterables and Iteration
- **For loop**: `for (let i = 0; i < arr.length; i++) { ... }`
- **For...of loop**: `for (let element of arr) { ... }`
- **While loop**: `while (condition) { ... }`
### Iterators
- **Iterator protocol**: Objects implementing the `next()` method.
- **Iterable**: Objects implementing the `[Symbol.iterator]()` method.
```javascript
let arr = [1, 2, 3];
let iterator = arr[Symbol.iterator]();
console.log(iterator.next().value); // 1
```
### Higher-order Functions
- **map, filter, reduce**
```javascript
let numbers = [1, 2, 3, 4, 5];
let doubled = numbers.map(x => x * 2); // [2, 4, 6, 8, 10]
let evens = numbers.filter(x => x % 2 === 0); // [2, 4]
let sum = numbers.reduce((acc, curr) => acc + curr, 0); // 15
```
### Strings
- **Concatenation**: `"Hello " + "World"`
- **Template Literals**: `` `Hello ${name}` ``
- **String Methods**: `str.toUpperCase()`, `str.includes()`
### Lists (Arrays)
- **Mutation**: `arr.push()`, `arr.pop()`, `arr.sort()`
- **Iteration**: `arr.forEach()`
### Dictionaries (Objects)
- **Access**: `obj.key`, `obj['key']`
- **Methods**: `Object.keys(obj)`, `Object.values(obj)`, `Object.entries(obj)`
### Sets
- **Creation**: `let mySet = new Set([1, 2, 3]);`
- **Methods**: `mySet.add(4)`, `mySet.has(2)`, `mySet.delete(3)`
### Errors
- **Try-Catch**:
```javascript
try {
// code that may throw an error
} catch (error) {
// code to handle the error
} finally {
// code to run regardless of error
}
```
### Modules
- **Importing and Exporting**
```javascript
// In module.js
export function greet() {
console.log("Hello, World!");
}
// In another file
import { greet } from './module.js';
greet(); // Hello, World!
```
### JSON
- **Parse**: `JSON.parse()`
- **Stringify**: `JSON.stringify()`
### File Handling
- **Reading and Writing Files**: Typically done using Node.js in a server environment.
### Example Translations
#### If-Else
Python:
```python
if condition:
# code
elif condition:
# code
else:
# code
```
JavaScript:
```javascript
if (condition) {
// code
} else if (condition) {
// code
} else {
// code
}
```
#### Functions
Python:
```python
def add(a, b):
return a + b
```
JavaScript:
```javascript
function add(a, b) {
return a + b;
}
// or using arrow function
const add = (a, b) => a + b;
```
#### For Loop
Python:
```python
for i in range(5):
print(i)
```
JavaScript:
```javascript
for (let i = 0; i < 5; i++) {
console.log(i);
}
```