Javascript & Python-Learning by comparison-part 1
Tags: javascript, python, learning, productivity
Published: 2023-08-24 12:51:30


Learning by comparing two programming languages can be beneficial in several ways. It helps you understand the underlying principles of programming, as you explore how different languages handle concepts like data types, control structures, and functions. Comparing languages also enhances your adaptability, enabling you to switch between languages based on project requirements. Moreover, it encourages critical thinking by analyzing the strengths and weaknesses of each language for specific tasks. This approach fosters a broader perspective on programming paradigms and problem-solving techniques, making you a more versatile developer.

So let us dive into some of the differences for some key aspects of the two languages:

## Hoisting:
Hoisting is a concept that exists in JavaScript but doesn't have an exact equivalent in Python due to the differences in how the two languages handle variable declaration and scope.

For example:

```javascript
console.log(x); // Outputs: undefined
var x = 5;
```

In this case, the variable `x` is hoisted to the top of the scope, so the `console.log` statement doesn't result in an error. However, `x` is `undefined` at that point.

Function declarations are also hoisted:

```javascript
foo(); // Outputs: "Hello"

function foo() {
    console.log("Hello");
}
```

**Hoisting in Python:**
Python doesn't have the same hoisting behavior as JavaScript. In Python, variables must be defined before they are used, and they are in scope from the point of definition onward. There's no concept of moving variable declarations to the top of the scope.

For example:

```python
print(x)  # Raises an error: NameError: name 'x' is not defined
x = 5
```

Similarly, function definitions must appear before they are used, but they don't need to be defined before the point of use like in JavaScript.

```python
foo()  # Raises an error: NameError: name 'foo' is not defined

def foo():
    print("Hello")
```

In Python, variables and functions need to be defined in the order in which they are used in the code.

In summary, hoisting is a behavior specific to JavaScript, and Python doesn't exhibit the same behavior due to its different scoping and variable declaration rules.
## Closures:
Closures exist in both JavaScript and Python, and they share similar concepts, but there are also some differences in how they are implemented and used in each language.

**Similarities:**
1. **Encapsulation:** In both languages, closures allow you to encapsulate data and behavior within a function, preserving the state even after the outer function has completed execution.
2. **Access to Outer Scope:** Closures in both languages have access to variables from their containing (enclosing) function's scope, even after that function has returned.

**Differences:**
1. **Syntax:** The syntax for defining closures is slightly different. In JavaScript, closures are often created using anonymous functions or arrow functions. In Python, closures are created by defining a nested function within another function.
2. **Variable Binding:** In JavaScript, variables in the closure's scope are bound by reference, meaning they can change if the outer variables change. In Python, variables in closures are usually bound by value, capturing the value of the variable at the time the closure is created.
3. **Late Binding in JavaScript:** JavaScript closures exhibit late binding behavior. This means that if the closure uses a variable from an outer scope and that variable changes after the closure is created, the closure will reflect the updated value when executed. Python closures tend to be more predictable in this regard.
4. **Scope Chain Differences:** JavaScript has a more complex scope chain due to its prototypal nature and lexical scoping rules, which can affect how closures access variables. Python's scoping rules are generally simpler.
5. **Function Closures:** In Python, closures are often used for their encapsulation and state-retention properties. In JavaScript, closures are heavily used to manage asynchronous operations and callbacks due to the language's asynchronous nature.
6. **Use Cases:** While both languages use closures for encapsulation and maintaining state, JavaScript closures are commonly used for handling asynchronous operations, event listeners, and callback functions, while Python closures are often used for encapsulation and cleaner code organization.

## Function expressions:
Function expressions exist in both JavaScript and Python, but there are differences in how they are defined and used in each language.

**Function Expressions in JavaScript:**
In JavaScript, a function expression is a way to define a function as part of an expression, typically by assigning it to a variable. This allows you to create anonymous functions or functions with a specific scope. Here's an example of a function expression in JavaScript:

```javascript
const add = function(a, b) {
    return a + b;
};

console.log(add(2, 3)); // Outputs: 5
```

In JavaScript, you can also use arrow function expressions:

```javascript
const multiply = (a, b) => a * b;

console.log(multiply(2, 3)); // Outputs: 6
```

**Function Expressions in Python:**
In Python, you can define functions using both the `def` keyword (function statement) and the `lambda` keyword (lambda function). The lambda function is similar to an anonymous function expression in JavaScript, although it's more limited in its capabilities. Here's an example of both types of function expressions in Python:

Using `def` keyword:

```python
def add(a, b):
    return a + b

print(add(2, 3))  # Outputs: 5
```

Using `lambda` keyword:

```python
multiply = lambda a, b: a * b

print(multiply(2, 3))  # Outputs: 6
```

**Differences:**
1. **Syntax:** JavaScript function expressions often involve assigning anonymous functions to variables, while in Python, both named functions (using `def`) and anonymous functions (using `lambda`) are part of the language's syntax.
2. **Scoping:** In JavaScript, function expressions have their own scope, which can help create closures and manage variable lifetimes. Python functions, whether defined using `def` or `lambda`, follow Python's scoping rules.
3. **Lambda Functions:** In Python, `lambda` functions are limited to a single expression and have more constrained capabilities compared to full function definitions. In JavaScript, function expressions can be as complex as regular named functions.
4. **Closures:** JavaScript function expressions are often used to create closures, which is a common use case. Python also supports closures, and functions defined within functions can capture variables from their enclosing scope.

## Objects:
In Python, a class is a blueprint for creating objects, while in JavaScript, an object can be directly created without the need for a class. Let's compare classes in Python with objects in JavaScript:

**Python Class:**
```python
class Car:
    def __init__(self, make, model):
        self.make = make
        self.model = model

    def get_info(self):
        return f"{self.make} {self.model}"

my_car = Car("Toyota", "Camry")
print(my_car.get_info())  # Outputs: "Toyota Camry"
```

In Python, classes are used to define the structure and behavior of objects. They can have attributes and methods associated with them. Objects are instances of classes, and they encapsulate data and functionality.

**JavaScript Object:**
```javascript
const car = {
    make: "Toyota",
    model: "Camry",
    getInfo: function() {
        return `${this.make} ${this.model}`;
    }
};

console.log(car.getInfo());  // Outputs: "Toyota Camry"
```

In JavaScript, objects can be created directly using object literals. They can have properties (similar to attributes in Python) and methods (functions associated with the object). JavaScript does not require a class to define an object; you can create objects and add properties and methods to them directly.

**Differences:**
1. **Class Requirement:** In Python, you need to define a class to create objects with a predefined structure and methods. In JavaScript, you can create objects directly using object literals without defining a class.
2. **Class-Based Inheritance:** Python supports class-based inheritance, where classes can inherit properties and methods from other classes. JavaScript also supports inheritance through prototype-based objects, but the approach is different from Python's class inheritance.
3. **Instance Methods:** In Python, instance methods take `self` as the first parameter to reference the instance. In JavaScript, methods can access instance data using the `this` keyword.
4. **Constructor:** In Python, the `__init__` method serves as the constructor. In JavaScript, you can define a constructor using the `constructor` property of an object or by setting up properties and methods directly.
5. **Encapsulation:** Python's class system enforces encapsulation, which means that access to attributes is controlled through methods. JavaScript's object properties can be directly accessed and modified.

In summary, while both Python classes and JavaScript objects are used to represent and organize data with associated behavior, the way they are defined and utilized is different due to the contrasting programming paradigms of the two languages. Python relies on classes to create objects, while JavaScript allows for more flexibility in creating objects directly using object literals.

## Constructors:
Constructors in JavaScript and Python are used to create objects, but they have some differences in how they are defined and used.

In JavaScript, constructors are typically defined as functions and are used with the `new` keyword to create instances of objects. For example:

```javascript
function Person(name, age) {
    this.name = name;
    this.age = age;
}

const person1 = new Person("Alice", 25);
```

In Python, constructors are defined using the `__init__` method within a class, and they are automatically called when an object is created. For example:

```python
class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

person1 = Person("Alice", 25)
```

One key difference is that in JavaScript, any function can act as a constructor if called with the `new` keyword, whereas in Python, constructors are specifically defined within a class using the `__init__` method.

Additionally, JavaScript's prototype-based inheritance system can sometimes lead to confusion, while Python's class-based system is more straightforward for managing objects and their properties.

This concludes our current discussion on learning by comparison.Stay engaged and keep an eye out for the next parts.