Advanced Javascript

Question 1

What is the main idea behind functional programming?

Answer 1

Functional programming aims to bring the precision, consistency, and predictability of mathematical functions into our programming environment. This means striving for “pure” functions that always produce the same output given the same input and do not cause side effects, like altering global state. This emphasis on predictability and consistency can make functional programs easier to test, debug, and understand.

Question 2

What are the three main concepts behind functional programming?

Answer 2

The three main concepts behind functional programming are immutability, separation of functions and data, and the use of first-class functions.

Immutability: This is the idea that once a data structure is created, it cannot be changed. Any ‘changes’ to the structure result in a new structure being created, leaving the original untouched. This avoids issues with shared state and reduces bugs, especially in concurrent and parallel programming.

Separation of functions and data: In functional programming, data and functions are kept separate. Functions take in data as arguments and produce new data as output, without modifying the original data.

First-class functions: This means functions in the language are treated as any other variable. They can be assigned to variables, stored in data structures, passed as arguments to other functions, and returned as values from other functions.

Question 3

What is immutability in the context of functional programming?

Answer 3

In functional programming, immutability refers to the concept that once a value is assigned to a variable, it cannot be changed. This means that once a variable is defined, its value stays the same throughout the entire program.

Question 4

What are the advantages of using immutability in functional programming?

Answer 4

Predictability: With immutability, a variable’s value is constant once assigned, which eliminates concerns about variables’ values changing unpredictably during the execution of a program. This consistency makes the program easier to understand and debug.

Single Source of Truth: An immutable set of data serves as a single source of truth.

Mutation tracking: Immutability facilitates the process of identifying changes in data over time by making use of reference and value equality, which simplifies the identification of changes.

Question 5

In functional programming, how do you manage situations where you need to update a value, given the concept of immutability?

Answer 5

In functional programming, when a value needs to be updated, a new variable is defined to represent the updated data, leaving the original data unchanged. This way, immutability is preserved, and you still have access to the original data, making it easier to trace the changes and understand the evolution of the data.

Question 6

What does the separation of data and functions mean in functional programming?

Answer 6

The concept of separating data and functions refers to the idea that data (like variables, arrays, and objects) and functions (the operations we can apply to data) exist independently of each other. Functions operate on data by taking it as input and returning a modified copy (respecting immutability) rather than altering the original data in-place.

Question 7

What is the effect of the rule of immutability on functions in functional programming?

Answer 7

In functional programming, the rule of immutability states that data cannot be changed once it’s created. This principle directly impacts how functions operate on data. Instead of altering the original data functions in functional programming return a modified copy of the data. This approach respects immutability and prevents side effects (unexpected changes to program state), leading to code that is easier to understand, test, and debug.

Question 8

What is a first-class function?

Answer 8

A first-class function is a function that can be treated like any other data type in a programming language. This means that first-class functions can be assigned to variables, stored in data structures, passed as arguments to other functions, and returned as results from other functions.

Question 9

What is the limitation of the const keyword in enforcing immutability in JavaScript?

Answer 9

In JavaScript, while the const keyword prevents reassigning a variable to a new value, it does not ensure complete immutability, especially when it comes to arrays and objects. We can still change the individual elements of an array or properties of an object that’s been declared with const.

Question 10

What is ESLint and how can it help ensure immutability in JavaScript?

Answer 10

ESLint is a tool for identifying and reporting patterns found in ECMAScript/JavaScript code. It can be used to enforce coding rules and styles. When used with the ESLint-plugin-immutable, it can help in identifying and preventing mutations in JavaScript code, thereby enforcing immutability.

Question 11

What is a closure in JavaScript?

Answer 11

A closure in JavaScript is a feature where a function returned from another function retains access to the scope of the function that created and returned it. This means that the returned function can still reference variables from the outer function’s scope, even after the outer function has completed execution.

Question 12

Why are closures useful in JavaScript?

Answer 12

In programming, a closure is a combination of a function and the lexical environment in which it was created. It allows a function to remember and access its lexical scope, even when that function is executing outside its lexical scope.

Closures are useful because they enable data encapsulation, provide a way to maintain persistent state within functions, allow for the creation of private variables and functions, and facilitate the use of callback functions by preserving the context and state of operations.

Question 13

What is the single responsibility principle and why is it important?

Answer 13

The single responsibility principle is a programming concept that suggests every module, class, or function should have responsibility over a single part of the functionality provided by the software. This principle is important as it makes code more readable, maintainable, and easier to test or debug, as each piece of code has only one job to do.

Question 14

What are higher-order functions in JavaScript?

Answer 14

Higher-order functions in JavaScript are functions that can receive other functions as arguments and/or return them as results.

Question 15

What is the reduce function in JavaScript used for ?

Answer 15

The reduce function in JavaScript is used to transform an array into a single value, such as the sum, average, or product of its elements.

Question 16

What is partial application in programming and how is it beneficial?

Answer 16

Partial application is a technique in programming where a function that takes multiple arguments is transformed into a function with fewer arguments by fixing some of the arguments to certain values. Partial application can be beneficial when we use a function often in our code and some of the arguments rarely change. By fixing those arguments, we can create a more specific function with fewer arguments to manage.

function multiply(x, y, z) {
    return x * y * z;
}

function multiplyByTwoAndThree(z) {
    return multiply(2, 3, z);
}

let result = multiplyByTwoAndThree(4); 

Question 17

What is recursion in programming?

Answer 17

Recursion in programming refers to a method where a function calls itself to solve a problem. Each time the function calls itself, it does so with a smaller or simpler version of the problem until it reaches a base condition which stops the recursion.

Question 18

What is ‘recursion depth’ and why is it important?

Answer 18

Recursion depth refers to the number of times a recursive function calls itself before reaching the base case. It’s an important consideration in recursion as deep recursion can lead to a stack overflow error, particularly in languages or environments that don’t optimize for recursive calls.

Question 19

What do the call and apply methods of a function in JavaScript do?

Answer 19

The call and apply methods in JavaScript are used to invoke a function. The call method takes arguments separately, while the apply method takes arguments as an array. Both methods can also take an initial argument to set the value of ‘this’ within the function

Call example:

object.objectMethod.call( objectInstance, arguments )

Apply example:

object.objectMethod.apply(objectInstance, arrayOfArguments)

Question 20

What is the class pattern in JavaScript?

Answer 20

The class pattern in JavaScript is a design pattern that allows us to define a blueprint for a specific type of object. This blueprint, or class, defines properties and methods common to all objects of this type.

Question 21

What is a constructor in JavaScript classes?

Answer 21

A constructor is a special method in a JavaScript class that gets automatically called when a new instance of the class is created. It’s used to initialize the properties of the object.

Question 22

What are JavaScript design patterns and why are they useful?

Answer 22

JavaScript design patterns are reusable solutions to common problems in software design. They serve as templates that can help write efficient, maintainable, and scalable code. Design patterns are beneficial as they promote code reuse and efficiency, improve understandability, and help prevent common issues by offering well-proven and tested solutions.

Question 23

What is the Constructor Pattern in JavaScript?

Answer 23

The Constructor Pattern in JavaScript involves creating a class and then using that class to create an extended class. The extended class can inherit properties from the parent class and also add new properties.

Question 24

What does the Constructor Pattern allow you to do with classes?

Answer 24

The Constructor Pattern allows you to create a class and then create an extended class from it, inheriting properties and methods, and potentially adding more properties or methods. This is useful when you want to create multiple subcategories of a class.

Question 25

What is the **super** keyword used for in JavaScript?

Answer 25

The super keyword in JavaScript is used within the **constructor** of a **subclass** to call the constructor of the **parent** class. It allows access to the **parent class's properties** and **methods**

Question 26

What is the Singleton Pattern in JavaScript?

Answer 26

The Singleton Pattern in JavaScript ensures that a **class** has only **one instance**, and provides a **global point of access** to it. When you try to create a new instance of a class that is a singleton, it returns the **existing** **instance**.

Question 27

What is the use case for the Singleton Pattern and why is it sometimes useful?

Answer 27

The Singleton Pattern is particularly useful when exactly **one objec**t is needed to **coordinate actions** across the system. It provides a way to wrap a unique instance of a class to ensure it is **accessed globally** and **cannot be re-instantiated**.

Question 28

What is the Factory Pattern in JavaScript?

Answer 28

The Factory Pattern in JavaScript is a design pattern which provides a way to **create objects** without needing to use the constructor of the class that will be created. It involves a **factory** method that handles the creation of objects based on the **input** it receives.

Question 29

What is the Abstract Factory pattern in JavaScript?

Answer 29

The Abstract Factory pattern is a **creational design pattern** that allows you to produce families of **related** objects without specifying their concrete classes. In JavaScript, an Abstract Factory might be a **function** that accepts **criteria** and returns a concrete object from one of several factories.

Question 30

What is a callback function in JavaScript and why is it useful?

Answer 30

A callback function in JavaScript is like any other function, but it is designed to be passed as an **argument** to another function and is **executed** ("called back") within that function. This can be used to ensure certain code doesn't run until other code has finished execution, which is particularly useful in **asynchronous** operations such as making API calls.

Question 31

What are "Creational design patterns" in programming?

Answer 31

Creational design patterns are a set of design patterns in software development that focus on **object creation mechanisms**. These patterns provide general solutions to create objects in a **flexible** and **reusable** way. Creational design patterns address various **object creation scenarios**, such as creating objects in a **controlled manner**, **hiding** the **complexity** of object creation, and providing ways to create objects based on **specific conditions** or **configurations**.

Question 32

What are "Structural design patterns" in programming?

Answer 32

Structural design patterns are concerned with **how** classes and objects are **composed** to form **larger structures**. They provide a way to ensure that changes in one part of a system **don't require** changes to the **entire system**, and help** fit parts** of the system together that might **not naturally** fit together.

Question 33

What is a module in JavaScript and why do we use them?

Answer 33

A module is a function or group of similar functions. They are grouped together within a file and contain the code to execute a specific task when called into a larger application. We use them to better organize and structure the codebase. They're useful for breaking down large programs into smaller, more manageable, and more independent chunks of code which carry out a single or a couple of related tasks.

Question 34

What is a mixin in JavaScript?

Answer 34

In JavaScript, mixins refer to a way of combining the properties and methods from multiple objects into a single object. They allow for the reuse of code enable you to **enhance the functionality** of an object or class **without altering** the **original class definition**. Mixins are not a built-in feature of JavaScript, but rather a programming pattern that can be implemented using various techniques.

Question 35

Why are mixins useful in Javascript?

Answer 35

**Code reuse:** Mixins allow you to define reusable behavior that can be easily applied to multiple objects instead of duplicating code across different objects. **Flexibility:** Mixins enable you to compose objects with different sets of behaviors by selecting and combining relevant mixins. This provides a flexible way to customize and extend objects without the need for complex inheritance hierarchies. **Avoiding inheritance limitations:** JavaScript has single inheritance, meaning an object can inherit from only one prototype. Mixins provide a way to overcome this limitation by allowing objects to inherit from multiple sources.

Question 36

How do you apply a mixin to an existing object or class in JavaScript?

Answer 36

A mixin can be applied to an existing object or class in JavaScript using the **Object.assign()** method. This method takes the **target object **(or **class prototype**) and the **source object** (the **mixin**) as arguments and **copies** the properties from the **source to the target**.

Question 37

What is a facade pattern in programming and why is useful?

Answer 37

The facade pattern in programming is a structural **design pattern** that provides a simplified interface to a complex system. It hides the complexities of the larger system and provides a simpler interface to the client. It's useful because it helps to reduce complexity and improve readability of code.

Question 38

What is the flyweight pattern in programming?

Answer 38

The flyweight pattern in programming is a **design pattern** used to **minimize memory** use by sharing data across similar objects. It prevents **unnecessary duplication of data** in memory.

Question 39

How is the flyweight pattern both similar and dissimilar to the Singleton pattern?

Answer 39

The flyweight pattern is similar to the Singleton pattern in that they both aim to **reduce unnecessary duplication**. However, while the Singleton pattern ensures there is only **one instance** of a class, the flyweight pattern focuses on **sharing data between instances** to reduce memory usage.

Question 40

What is the Model-View-Controller (MVC) pattern in software design and what are the different parts responsible for?

Answer 40

The MVC pattern is a design pattern that separates an application into **three** main logical components: the **model**, the **view**, and the **controller**. This pattern is used to isolate the concerns of **data** (model), **user interface** (view), and **control flow** (controller) to promote organization and scalability. The **model** is responsible for managing the **data** of the application. The view is responsible for **presenting** the data to the user, often as a user interface. The controller handles **user input**, interacts with the model to **fetch or update data**, and **updates the view** accordingly.

Question 41

What is the Model-View-ViewModel (MVVM) pattern and where is it commonly used?

Answer 41

The MVVM pattern is a design pattern that separates an application into **three** components: the **View**, the **ViewModel**, and the **Model**. The **View** represents the **user interface**, the **ViewModel** manages the **logic** and the **state** of the **data**, and the **Model** interacts with the **back-end** for data processing. The MVVM pattern is commonly used in applications developed with frameworks like **React** and Angular. In React, for instance, **stateless components** represent the **View**, **stateful components** act as the **ViewModel**, and the **Model** is where React **connects to the back-end** to process data.

Question 42

What is the Observer pattern and where is it commonly used?

Answer 42

The Observer pattern is a behavioural **design pattern** that offers a **subscription model** in which **objects subscribe** to an **event** and **get notified** when the **event occurs**. This pattern is the most commonly used in **event driven systems**.

Question 43

What is the State pattern?

Answer 43

The State pattern is a behavioural **design pattern** that allows an **object to change** its behavior when its i**nternal state changes**. In web development, this often means **re-rendering** parts of the application when the **data** they **depend** on **changes**.

Question 44

What is the 'base case' in recursion?

Answer 44

The base case in recursion is the condition that **stops the function** from calling itself endlessly. It defines the point where the function should **stop** making **recursive calls** and start **returning results**.

Question 45

What is a stack overflow and how can you prevent it?

Answer 45

A stack overflow occurs when a program uses **more memory** than the **call stack** has **available**, usually because of **infinite recursion**. When a stack overflow happens, the program **can't create new instances** of functions, and this may cause the program and the computer to **crash**. To prevent stack overflow in recursive functions, you need to ensure that **each recursive call changes the state** of the program in a way that **moves closer** to the **base case**. The base case must eventually be reached to stop further recursive calls.

Question 46

How is tail recursion different from head recursion and which one is more efficient?

Answer 46

In tail recursion, the **processing** happens **before** the **recursive** call. In head recursion, the **recursive** call happens **first**, and the **processing** happens **after**. **Tail** recursion is more **efficient** because the computer can **forget** about the **earlier steps** once they are done. In head recursion, the computer has to **remember all** the steps, which can use up a lot of **memory**.

Question 47

Define "memoization" in the context of computer programming.

Answer 47

Memoization is an **optimization technique** used primarily to **speed up** programs by **storing** the **results** of **expensive** function calls and **reusing** them when the **same inputs** are used again. It is a form of **caching** where computed results are stored for future use.

Question 48

Can you detail the process of how memoization works?

Answer 48

Memoization works by maintaining a map or an array (a **cache**) to **keep track** of **previously** computed **results** of a function call. When a function is called, the memoization procedure **checks the cach**e to see if the result for the **given input** is already available. If it is, the **cached result is returned**, bypassing the execution of the function's logic. If the result isn't in the cache, the **function is executed**, the **result is cached**, and then returned. This technique **optimizes** the program execution by **avoiding unnecessary recomputation**.