JavaScript Array Methods and Scoping
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Questions and Answers

Considering the code snippet for creating an object using the Object.create() method, what does the following code accomplish? console.log(person.age)

  • It prints the value of `age` property of the `person` object, which is 30, assigned directly to the object.
  • It prints the value of `age` property of the `person` object, which is 30, defined within the `Object.create()` method.
  • It throws an error because `age` is not a property of the `person` object.
  • It prints the value of `age` property of the `person` object, which is 30, inherited from the prototype. (correct)

    • When creating an object using the ES6 class syntax (as shown in the content), what does this refer to inside the constructor function?

  • The `constructor` function itself.
  • The global object.
  • The `Person` class itself.
  • The newly created object (`user` in this case). (correct)

    • The Object.assign() method and the spread operator (...) are used for copying properties between objects. What is the key difference between them?

  • `Object.assign()` copies all properties, including non-enumerable properties, while the spread operator only copies enumerable properties. (correct)
  • There's no significant difference, they are essentially the same in terms of functionality.
  • `Object.assign()` only works for objects, while the spread operator can work with arrays and objects.
  • The spread operator copies by reference, while `Object.assign()` copies by value.

    • In the context of JavaScript, what does the term 'currying' refer to?

    <p>A technique for converting a function with multiple arguments into a sequence of functions, each taking a single argument. (B)</p> Signup and view all the answers

    What is a key difference between regular functions and arrow functions in JavaScript?

    <p>Regular functions have their own binding for the <code>this</code> keyword, while arrow functions inherit the <code>this</code> binding from the enclosing scope. (A)</p> Signup and view all the answers

    Which of the following JavaScript object creation methods directly assigns properties to the object without using a prototype or constructor?

    <p>Object Literal (B)</p> Signup and view all the answers

    When discussing object creation in JavaScript, what is a key difference between Object.create() and the ES6 class syntax?

    <p><code>Object.create()</code> uses prototypes for inheritance, while ES6 classes rely on constructor functions. (C)</p> Signup and view all the answers

    In the context of JavaScript, what does the this keyword refer to when used within a method of an object created using a factory function?

    <p>The object on which the method is called. (D)</p> Signup and view all the answers

    What does the term 'Rejected' signify in an operation?

    <p>The operation failed. (D)</p> Signup and view all the answers

    Which statement accurately describes a prototype in JavaScript?

    <p>A prototype is an object from which other objects inherit properties. (D)</p> Signup and view all the answers

    What role does the proto property serve in JavaScript?

    <p>It allows an object to inherit properties from another object. (B)</p> Signup and view all the answers

    How do setters enhance the integrity of object properties in JavaScript?

    <p>They perform validation before modifying a property. (C)</p> Signup and view all the answers

    What is the primary function of the event loop in JavaScript?

    <p>To manage synchronous and asynchronous operations. (C)</p> Signup and view all the answers

    What does implicit type conversion in JavaScript mean?

    <p>It is when JavaScript automatically converts a value to a different type based on context. (D)</p> Signup and view all the answers

    What is one key benefit of using getters in JavaScript?

    <p>They encapsulate the logic for retrieving property values. (A)</p> Signup and view all the answers

    Which of the following is a characteristic feature of JavaScript's prototype-based inheritance?

    <p>Every function automatically has a prototype property. (B)</p> Signup and view all the answers

    What is the primary purpose of the try statement in error handling?

    <p>To write code that might throw an error. (C)</p> Signup and view all the answers

    What does the catch block do when an error is thrown in the try block?

    <p>It allows handling of the error that occurred in the try block. (A)</p> Signup and view all the answers

    In terms of data encapsulation, why are getters and setters preferred?

    <p>They provide controlled access to properties, enforcing rules. (D)</p> Signup and view all the answers

    What is the role of the finally statement in error handling?

    <p>It contains code that runs regardless of whether an error occurred. (C)</p> Signup and view all the answers

    What is a throw statement used for?

    <p>To manually create and throw an error. (B)</p> Signup and view all the answers

    What can be included within an Error object?

    <p>Information about the error, such as message and stack trace. (B)</p> Signup and view all the answers

    What is the initial state of a Promise object?

    <p>Pending. (D)</p> Signup and view all the answers

    What does it mean when a Promise is Fulfilled?

    <p>The operation was completed successfully. (A)</p> Signup and view all the answers

    What is the primary benefit of using JavaScript for handling multiple I/O operations?

    <p>It ensures that the main thread remains free from long-running tasks. (C)</p> Signup and view all the answers

    What does array destructuring allow you to do in JavaScript?

    <p>Extract values from an array and assign them to variables. (D)</p> Signup and view all the answers

    Which statement best describes the differences between cookies, local storage, and session storage?

    <p>Session storage has a limited lifespan and is cleared when the session ends. (B)</p> Signup and view all the answers

    Which method is used to add an event listener to an element in JavaScript?

    <p>addEventListener() (D)</p> Signup and view all the answers

    Which JavaScript array method removes the first element from an array?

    <p>shift (B)</p> Signup and view all the answers

    What is the purpose of the stopPropagation() method in event handling?

    <p>It stops the event from reaching parent elements' handlers. (A)</p> Signup and view all the answers

    What is true about the 'const' declaration in JavaScript?

    <p>It is block-scoped. (D)</p> Signup and view all the answers

    How does event delegation benefit your JavaScript code?

    <p>It simplifies managing several similar event handlers by centralizing them. (D)</p> Signup and view all the answers

    Which of the following statements is NOT true regarding object destructuring in JavaScript?

    <p>It can only be applied to arrays, not objects. (D)</p> Signup and view all the answers

    Which approach is NOT a way to create an object in JavaScript?

    <p>JSON.parse() (C)</p> Signup and view all the answers

    What describes the Temporal Dead Zone (TDZ) in JavaScript?

    <p>The time before a variable is declared and can be accessed. (C)</p> Signup and view all the answers

    When using inline event handlers in HTML, what is a common disadvantage?

    <p>They are less readable and harder to maintain. (A)</p> Signup and view all the answers

    Which of the following statements about 'let' is true?

    <p>It cannot be accessed before declaration due to hoisting. (C)</p> Signup and view all the answers

    What does the 'push' method do in a JavaScript array?

    <p>Adds a new element to the end of the array. (A)</p> Signup and view all the answers

    How can you convert an array to an object in JavaScript effectively?

    <p>Using Object.assign() with a rest parameter (D)</p> Signup and view all the answers

    Which of the following is a characteristic feature of 'var' in JavaScript?

    <p>Function-scoped. (B)</p> Signup and view all the answers

    Which of the following is NOT a benefit of using arrow functions in JavaScript?

    <p>Availability of arguments object (C)</p> Signup and view all the answers

    In the context of JavaScript functions, what does the term 'lexical this' refer to?

    <p>The value of 'this' within the function's surrounding scope (D)</p> Signup and view all the answers

    Which operator performs type coercion before comparing two values for equality?

    <p>== (B)</p> Signup and view all the answers

    What is the primary difference between a regular function and an arrow function in JavaScript?

    <p>Regular functions have their own 'this' binding, while arrow functions inherit 'this' from the surrounding scope (D)</p> Signup and view all the answers

    Consider the following code snippet: javascript const obj = { name: 'Alice', greet: function() { console.log(this.name); } }; obj.greet(); What will be printed to the console?

    <p>Alice (D)</p> Signup and view all the answers

    Identify the correct syntax for declaring a regular function in JavaScript.

    <p>function name(parameters) { ... } (B), function(parameters) { ... } (D)</p> Signup and view all the answers

    What is a possible consequence of using the '==' operator to compare values in JavaScript?

    <p>Type coercion can lead to unexpected or unintended comparison results (A)</p> Signup and view all the answers

    Which of the following best describes implicit type coercion in JavaScript?

    <p>Automatically converting values to a common data type during an operation (C)</p> Signup and view all the answers

    Flashcards

    Object.create()

    Creates a new object with specified prototype properties.

    ES6 Classes

    A syntax in JavaScript for creating objects and dealing with inheritance.

    Factory Function

    A function returning an object, allowing multiple instances with different properties.

    Object Literal

    A way to define an object with key-value pairs directly.

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    Object.assign()

    Copies values from one or more source objects to a target object.

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    Spread Operator

    A syntax to expand iterable elements into a list.

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    this Keyword

    Refers to the context object that the function is executed in.

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    Currying

    Transforming a function of multiple arguments into a sequence of functions with single arguments.

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    Arguments Object

    An array-like object in regular functions that holds parameters.

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    Arrow Functions

    Functions that do not have their own arguments object, use rest parameters for access.

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    Regular Functions

    Functions declared with 'function' keyword, allowing access to arguments and this binding.

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    Loose Equality Operator (==)

    Compares values after converting them to the same type, allowing type coercion.

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    Strict Equality Operator (===)

    Compares both value and type without type coercion, ensuring strict matching.

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    This Binding in Functions

    In regular functions, 'this' refers to the object calling the function, set at runtime.

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    Arrow Functions This

    They do not create their own 'this', inheriting it from the surrounding context.

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    Implicit Type Coercion

    Automatic conversion of values to match types during comparisons in JavaScript.

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    Array mutation methods

    Methods that change the original array: pop, push, shift.

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    Var characteristics

    Global/function-scoped, can be updated and re-declared.

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    Let characteristics

    Block-scoped, can be updated but not re-declared; hoisted with TDZ.

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    Const characteristics

    Block-scoped, cannot be updated or re-declared, hoisted similarly to 'let'.

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    Temporal Dead Zone (TDZ)

    Period when 'let' and 'const' variables are not accessible until initialized.

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    Constructor Functions

    Functions used to create objects with specific properties.

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    Block scope

    Scope where 'let' and 'const' variables exist, limited to their block.

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    Rejected

    Indicates that an operation has failed.

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    Async Function

    A function that allows asynchronous programming in JavaScript.

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    Prototype

    An object from which other objects inherit properties and methods.

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    proto

    A property for inheriting from another object in JavaScript.

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    Getters and Setters

    Special methods for controlled access to object properties.

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    Setter

    A method that allows modifying a property with validation.

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    Event Loop

    The mechanism that handles asynchronous actions in JavaScript.

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    Inheritance in JavaScript

    The process by which objects acquire properties from other objects.

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    Implicit Type Conversion

    Automatic conversion of a value to a different data type by JavaScript based on context.

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    try Statement

    Code block where errors can occur; if an error appears, control moves to catch block.

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    catch Statement

    Block for handling errors thrown in the try block, with an optional error object parameter.

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    finally Statement

    Block that executes after try and catch, regardless of whether an error occurred.

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    throw Statement

    Used to create and throw a custom error, transferring control to the nearest catch block.

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    Error Object

    Object representing a runtime error, containing information like message and type.

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    Promise States

    The three states of a promise: Pending, Fulfilled, and Rejected.

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    Pending State

    Initial state of a promise; the operation hasn't completed yet.

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    Destructuring Assignment

    Extracts values from arrays or objects and assigns to variables.

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    Array Destructuring

    Allows extraction of elements from an array and assigns them to variables.

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    Object Destructuring

    Allows extraction of properties from an object and assigns them to variables.

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    Cookies vs Local Storage vs Session Storage

    Methods of storing data in a web browser with different limits and security.

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    addEventListener() Method

    A way to attach an event handler to an element.

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    stopPropagation() Method

    Stops an event from bubbling up to parent elements in the DOM.

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    Event Delegation

    Handling events at a higher level in the DOM tree.

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    I/O Operations in JavaScript

    JavaScript handles multiple I/O operations without blocking the main thread.

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    Study Notes

    JavaScript Array Methods

    • Changing original array:
      • pop: Deletes the last element.
      • push: Adds an element to the end.
      • shift: Deletes the first element.
      • slice: Creates a shallow copy (doesn't modify original).

    Converting Array to Object

    • Object.assign({}, ...arr): Creates a new object from an array using the rest operator.

    var, let, and const Differences

    • var:
      • Function-scoped.
      • Can be re-declared within the same scope.
      • Hoisted (declared before execution).
    • let:
      • Block-scoped.
      • Can't be re-declared within the same scope.
      • Hoisted (declared before execution), but not initialized; attempting to use it before declaration causes a "temporal dead zone" error.
      • Can be updated.
    • const:
      • Block-scoped.
      • Can't be re-declared or re-assigned.
      • Hoisted (declared before execution), but not initialized; attempting to use it before declaration causes a "temporal dead zone" error.

    Temporal Dead Zone

    • Short period during execution when let or const variables are inaccessible.
    • It occurs after the variable is declared but before it's initialized.

    Creating Objects in JavaScript

    • Constructor Functions:
      • Define a function that acts as a blueprint for creating objects.
      • Use new keyword to create instances of object from a class/function blueprint.
    • Object.create():
      • Creates a new object with a prototype.
    • Object Literals:
      • Creates objects using curly braces and key-value pairs.
    • Factory Functions:
      • Create objects from a function and return them.

    Copying Object Properties

    • Object.assign(): Copies properties from source to target
    • Spread Operator (...): Creates a new object by copying the properties of the source object

    this Keyword

    • Global context: Refers to the global object.
    • Methods: Refers to the object the method belongs to.
    • Constructor functions: Refers to the newly created object.
    • Event handlers: Refers to the element that triggered the event.
    • Arrow functions: Lexically bound to the surrounding scope.

    Currying

    • Technique to transform a function with multiple arguments into a sequence of functions, each taking a single argument.

    Regular vs. Arrow Functions

    • arguments object: Regular functions have access to this object, which stores the function's parameters. Arrow functions don't have their own arguments object, use rest parameters to achieve similar result.
    • this binding: In regular functions the this keyword is determined dynamically, in an arrow function it's lexically bound (from its surrounding scope).
    • Syntax: Regular functions define using the keyword "function", and can use either declaration or expression syntax. Arrow functions use concise syntax and the => operator

    Equality Operators (==, ===)

    • == (Loose Equality): Performs type coercion before comparison.
    • === (Strict Equality): Compares both value and type without coercion.

    Implicit Type Coercion

    • JavaScript automatically converts values to different data types based on the context in which they are used.

    Error Handling (try...catch...finally)

    • try block: Contains code that might throw an error.
    • catch block: Handles errors thrown in the try block.
    • finally block: Contains code that always runs, regardless of whether an error occurred or not.

    throw Statement

    • Used to manually create and throw an error.
    • Can create custom error messages/exceptions based on certain conditions.

    Error Objects

    • Contain information about the error such as message, type, stack trace.

    Promises

    • Represents the eventual completion or failure of an asynchronous operation.
    • Has three states: Pending, Fulfilled, Rejected.

    Async Functions

    • Used for asynchronous operations.

    Prototypes

    • Mechanism for creating objects, inheriting properties and methods from other objects.
    • Objects have a prototype property (proto).
    • __proto__: A property that refers to other objects in the prototype chain.

    Getters and Setters

    • Special methods to control object property access.
      • Getters: Retrieve values.
      • Setters: Update values.
    • Used to encapsulate internal logic and perform validation.

    Event Loop

    • The main part of JavaScript's non-blocking concurrency model.
    • Handles asynchronous operations efficiently without blocking the main thread.
      • Callbacks: Placed into the callback queue.
      • Execution: The event loop checks the call stack, processes the callback queue, and executes callbacks.

    Destructuring Assignment

    • Extracts values from arrays or objects and assigns them to variables efficiently.
      • Array Destructuring: Separate values from array using square brackets
      • Object Destructuring: Separate properties from objects using curly braces

    Storage Methods (Cookies, Local Storage, Session Storage)

    • Cookies: Store small pieces of data (up to 4KB). Accessible from client and server.
    • Local Storage: Stores larger amounts of data (up to 5MB-10MB). Stays persistent until deleted.
    • Session Storage: Stores data only for the duration of the browser session. Cleared when the tab closes.

    Event Listeners

    • addEventListener(): Method to add event listeners to elements dynamically.
    • Inline Event Handlers: Adding directly inside HTML attributes like <button onclick="...">.

    Event Propagation

    • How events propagate through document.
      • Capturing Phase: Root -> Target Element
      • Bubbling Phase: Target -> Root

    Event Delegation

    • Handling events at a higher level in the DOM tree.
    • Reduces the number of event listeners needed.

    stopPropagation()

    • Prevents an event from bubbling up the DOM tree.

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