JavaScript Overview and History
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Questions and Answers

What is the primary role of JavaScript in web development?

  • Server-side data management
  • Graphic design and layout
  • Database querying
  • Webpage behavior and client-side scripting (correct)

    • Which of the following best describes the typing discipline of JavaScript?

  • Dynamic and strong
  • Static and weak
  • Dynamic and weak (correct)
  • Static and strong

    • Who initially designed JavaScript?

  • Guido van Rossum
  • Brendan Eich (correct)
  • Tim Berners-Lee
  • James Gosling

    • Which standard does JavaScript conform to?

    <p>ECMAScript (A)</p> Signup and view all the answers

    What type of memory management does JavaScript use?

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

    Which of the following is NOT a major implementation of JavaScript?

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

    What programming paradigms does JavaScript support?

    <p>Event-driven, functional, imperative, and object-oriented (A)</p> Signup and view all the answers

    What is the first popular web browser that made JavaScript widely accessible?

    <p>Mosaic (A)</p> Signup and view all the answers

    What is the purpose of the same-origin policy in web security?

    <p>Prevent scripts from one site from accessing information on another site. (C)</p> Signup and view all the answers

    Which of the following is NOT a method to mitigate cross-site scripting (XSS) vulnerabilities?

    <p>Requiring cookies for all requests (A)</p> Signup and view all the answers

    Which project is designed specifically for safe embedding and isolation of third-party JavaScript and HTML?

    <p>Closure Toolkit (A)</p> Signup and view all the answers

    What issue arises with cross-site request forgery (CSRF)?

    <p>Victims' browsers can be tricked into making unintended requests. (C)</p> Signup and view all the answers

    What is one effective strategy for preventing CSRF attacks?

    <p>Requiring an authentication value in hidden form fields. (A)</p> Signup and view all the answers

    Which of the following defines a common issue with reflected XSS attacks?

    <p>URLs containing malicious scripts provided by attackers. (D)</p> Signup and view all the answers

    Which of the following best describes JavaScript hijacking?

    <p>Accessing private data through a &lt;script> tag on an attacker's site. (A)</p> Signup and view all the answers

    What security mechanism is primarily aimed at ensuring only trusted code runs on a webpage?

    <p>Content Security Policy (A)</p> Signup and view all the answers

    What programming language was initially intended to be embedded in Netscape Navigator along with Java?

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

    Which company created JScript, its own JavaScript interpreter?

    <p>Microsoft (A)</p> Signup and view all the answers

    Which year was the first ECMAScript language specification officially released?

    <p>1997 (B)</p> Signup and view all the answers

    What was the primary function of Ajax, as described by Jesse James Garrett in 2005?

    <p>To load data in the background without full page reloads (C)</p> Signup and view all the answers

    Which version of ECMAScript marked a significant advancement in JavaScript with extensive additions?

    <p>ECMAScript 6 (D)</p> Signup and view all the answers

    What was the significant change introduced by Google in its Chrome browser in 2008?

    <p>Just-in-time compilation (JIT) (B)</p> Signup and view all the answers

    What led to the stagnancy of client-side scripting in the early 2000s?

    <p>Internet Explorer's dominance (A)</p> Signup and view all the answers

    Who created Node.js, which enabled JavaScript to be used outside of web browsers?

    <p>Ryan Dahl (C)</p> Signup and view all the answers

    What was a major consequence of the differences between JavaScript and JScript for developers?

    <p>Difficulties in creating cross-browser compatible sites (A)</p> Signup and view all the answers

    What was the original name of JavaScript when it was first shipped?

    <p>LiveScript (C)</p> Signup and view all the answers

    Which browser's release in 2004 began the shift away from Internet Explorer's dominance?

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

    What was the main reason behind Netscape changing the name from LiveScript to JavaScript?

    <p>Improved branding and marketing (A)</p> Signup and view all the answers

    In what year did Netscape submit JavaScript to Ecma International?

    <p>1996 (B)</p> Signup and view all the answers

    What did the rise of Ajax and related technologies contribute to in web development?

    <p>The end of static web pages (A)</p> Signup and view all the answers

    What occurs when adding a number to a string in JavaScript?

    <p>The number is cast to a string and concatenated. (B)</p> Signup and view all the answers

    What does the unary + operator do to its operand?

    <p>Casts to a number. (D)</p> Signup and view all the answers

    Which of the following correctly describes JavaScript's typing system?

    <p>It is weakly typed and allows implicit typecasting. (C)</p> Signup and view all the answers

    What happens when an empty array is added to an empty object in JavaScript?

    <p>Returns '[object Object]'. (C)</p> Signup and view all the answers

    How does JavaScript handle object-oriented inheritance?

    <p>Using prototype chains instead of classes. (B)</p> Signup and view all the answers

    What does the eval function in JavaScript do?

    <p>Executes statements provided as strings at runtime. (C)</p> Signup and view all the answers

    In JavaScript, how does calling a function as a method affect the this keyword?

    <p>It binds to the object before the function call. (B)</p> Signup and view all the answers

    Which of the following best describes first-class functions in JavaScript?

    <p>Functions can be used as arguments and returned from other functions. (C)</p> Signup and view all the answers

    What is the result of adding the string '123' to the number 1 in JavaScript?

    <p>1231 (A)</p> Signup and view all the answers

    What is the result of subtracting a number from a string that cannot be converted to a number?

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

    What happens when the prototype of a function is modified?

    <p>New instances will inherit the modified properties. (D)</p> Signup and view all the answers

    How can prototype inheritance in JavaScript be simulated?

    <p>Through constructor functions and modifying prototypes. (C)</p> Signup and view all the answers

    What does the toString function do when defined on an object in JavaScript?

    <p>Alters how the object is displayed when converted to a string. (B)</p> Signup and view all the answers

    What is the primary distinction between functions and methods in JavaScript?

    <p>There is no distinction; it depends on how they are called. (D)</p> Signup and view all the answers

    What will be the output of invoking factorial(3)?

    <p>6 (B)</p> Signup and view all the answers

    Which statement regarding the creation of an HTML element is correct?

    <p>An element can be appended to the body after being created. (C)</p> Signup and view all the answers

    What will happen if you try to compute the factorial of a negative number using the factorial function?

    <p>It will return undefined. (C)</p> Signup and view all the answers

    Which of the following statements correctly describes arrow functions in JavaScript?

    <p>They shorten the syntax for writing functions. (C)</p> Signup and view all the answers

    How does the generate_multiplier_function work?

    <p>It can capture and retain state between invocations. (C)</p> Signup and view all the answers

    What will be the output of five_multiples(3) if five_multiples is returned from generate_multiplier_function(5)?

    <p>15 (A)</p> Signup and view all the answers

    Which of the following describes how to create a class in JavaScript?

    <p>Classes can contain methods that act on their instances. (B)</p> Signup and view all the answers

    What will happen in the factorial function if you provide a non-numerical argument?

    <p>It will log an error to the console. (D)</p> Signup and view all the answers

    What is the purpose of arguments in functions before ES6?

    <p>To access the parameters passed to the function. (A)</p> Signup and view all the answers

    What would be the output of the following function call: sum(1, 2, 3)?

    <p>6 (A)</p> Signup and view all the answers

    How would you define a closure in JavaScript?

    <p>A closure is when a function accesses variables from its outer scope. (B)</p> Signup and view all the answers

    What will the method myBall.show() log if myBall is an instance of Ball with a radius incremented from 5 to 6?

    <p>6 (B)</p> Signup and view all the answers

    What happens if you execute an arrow function with no parameters?

    <p>It returns undefined. (D)</p> Signup and view all the answers

    What is the primary purpose of a JavaScript engine?

    <p>To interpret and execute JavaScript code (D)</p> Signup and view all the answers

    What does the term 'Vanilla JS' refer to?

    <p>JavaScript written without any libraries or frameworks (A)</p> Signup and view all the answers

    Which JavaScript library is noted as the most widely used in web development?

    <p>jQuery (A)</p> Signup and view all the answers

    How does JavaScript handle multiple I/O operations?

    <p>Via an event loop managing a queue of messages (A)</p> Signup and view all the answers

    What is the significance of the letter circulated by Ryan Dahl in 2024 regarding JavaScript?

    <p>To call for the JavaScript trademark to be freed from Oracle (B)</p> Signup and view all the answers

    Which of the following applications is an example of a non-browser use of JavaScript?

    <p>Node.js server-side applications (D)</p> Signup and view all the answers

    What inspired the growth of server-side JavaScript usage in the late 2000s?

    <p>The launch of Node.js and similar frameworks (B)</p> Signup and view all the answers

    What is an example of client-side scripted behavior in JavaScript?

    <p>Loading new content without a page reload (B)</p> Signup and view all the answers

    What type of scope was initially the only option available in JavaScript before ECMAScript 2015?

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

    What feature is associated with ECMAScript as it pertains to JavaScript?

    <p>It serves as the standardized specification of the language (D)</p> Signup and view all the answers

    Which of the following statements best describes how JavaScript engines operate?

    <p>They communicate with rendering engines through the Document Object Model (D)</p> Signup and view all the answers

    What aspect of JavaScript allows it to handle multiple tasks without blocking the execution?

    <p>Asynchronous programming model with a callback queue (A)</p> Signup and view all the answers

    Which of the following JavaScript features was introduced in ECMAScript 2015?

    <p>Block scoping with 'let' and 'const' (A)</p> Signup and view all the answers

    What element distinguishes JavaScript from traditional compiled languages?

    <p>It uses asynchronous event handling (C)</p> Signup and view all the answers

    What is the purpose of closures in JavaScript?

    <p>To allow private properties and methods. (C)</p> Signup and view all the answers

    What will be the output of counter2.next() on the third call?

    <p>{value: 3, done: false} (C)</p> Signup and view all the answers

    Which of the following is NOT a way to export from a module?

    <p>Export private functions (B)</p> Signup and view all the answers

    What does the add() function do when imported?

    <p>It adds two numbers. (A)</p> Signup and view all the answers

    What is the purpose of the gcd() method in the LCMCalculator structure?

    <p>To provide the greatest common divisor. (B)</p> Signup and view all the answers

    How does the LCMCalculator ensure that the gcd function is only computed once?

    <p>By redefining the <code>gcd</code> method for the instance. (A)</p> Signup and view all the answers

    What will the toString() method return in the LCMCalculator class?

    <p>A string representation of a and b. (A)</p> Signup and view all the answers

    What is the significance of using yield in generator functions?

    <p>It pauses function execution and retains its context. (A)</p> Signup and view all the answers

    Which statement accurately reflects the use of destructuring assignment in the gcd method?

    <p>It is used to simplify the code by combining declaration and assignment. (C)</p> Signup and view all the answers

    How is the LCM calculated in the lcm method of the LCMCalculator?

    <p>By dividing the product by the greatest common divisor. (C)</p> Signup and view all the answers

    Which of the following is true about the dynamicCounter generator function?

    <p>It generates an infinite sequence of incrementing numbers. (C)</p> Signup and view all the answers

    What is a potential security concern mentioned regarding JavaScript?

    <p>JavaScript can execute scripts delivered through the Web. (A)</p> Signup and view all the answers

    What is the output of console.log(add(1,2)); after importing add from a module?

    <p>3 (D)</p> Signup and view all the answers

    Which of the following best describes a lexical closure in JavaScript?

    <p>It allows inner functions to access the variables of their outer functions even after the outer function has finished executing. (D)</p> Signup and view all the answers

    What is the main purpose of using the 'this' keyword within a function in JavaScript?

    <p>To access properties and methods of the object that is executing the current function. (B)</p> Signup and view all the answers

    Which of the following is a key feature of JavaScript promises?

    <p>They can only be resolved once and cannot be modified afterward. (D)</p> Signup and view all the answers

    What distinguishes variadic functions in JavaScript?

    <p>They can process an indefinite number of parameters. (B)</p> Signup and view all the answers

    What is the primary function of array and object literals in JavaScript?

    <p>To allow the use of less syntax when defining data structures. (A)</p> Signup and view all the answers

    How does JavaScript's prototype chain contribute to inheritance?

    <p>It automatically searches for methods along the prototype chain. (B)</p> Signup and view all the answers

    Which keyword is used in JavaScript to define a variable that cannot be reassigned?

    <p>const (C)</p> Signup and view all the answers

    What are promises in JavaScript designed to do?

    <p>They manage both successful and failed asynchronous actions. (A)</p> Signup and view all the answers

    Which of the following is a feature of the async/await syntax in JavaScript?

    <p>It simplifies asynchronous code to appear like synchronous code. (C)</p> Signup and view all the answers

    What happens when a variable is declared without a keyword in JavaScript?

    <p>It is defined globally. (B)</p> Signup and view all the answers

    Which of the following best describes the use of regular expressions in JavaScript?

    <p>They provide a complex syntax for text manipulation. (B)</p> Signup and view all the answers

    Which feature allows JavaScript functions to accept a varying number of arguments?

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

    What is the principal drawback of defining variables using 'var' in JavaScript?

    <p>Variables can potentially be redeclared in the same scope. (B)</p> Signup and view all the answers

    Which method is used to output data in JavaScript's runtime environment?

    <p>console.log() (B)</p> Signup and view all the answers

    Study Notes

    JavaScript Overview

    • JavaScript is a programming language for web development, alongside HTML and CSS.
    • 99% of websites use JavaScript on the client-side for webpage behavior.
    • Web browsers execute JavaScript code through dedicated JavaScript engines.
    • Engines are used in servers and apps. A popular non-browser runtime is Node.js.
    • High-level language; conforms to the ECMAScript standard.
    • Dynamically typed, prototype-based object-oriented, and supports multiple programming styles (imperative, functional, event-driven).
    • Offers APIs for text, dates, regular expressions, and the DOM. I/O (input/output), like networking and graphics, is provided via browser or runtime APIs.

    JavaScript History

    • JavaScript's origins lie in Netscape Navigator (1995).
    • Initially named LiveScript, changed to JavaScript.
    • Similar names to Java led to confusion, but JavaScript is distinct.
    • Microsoft's JScript emerged, causing browser compatibility problems initially.
    • JavaScript was submitted to Ecma International, leading to first ECMAScript spec.
    • Standard specification iterations (ECMAScript 2, 3, etc.) followed.
    • Firefox's development (2004) renewed focus on JavaScript.
    • Google Chrome's V8 engine (2008) accelerated development, boosting JIT compilation.
    • ECMAScript 5 (2009) unified efforts; further iterations led to ECMAScript 6 in 2015 and beyond.
    • Node.js (2009) allowed JavaScript use outside browsers.

    JavaScript Features

    • Typing: Dynamic and weak—types are associated with values, not variables. Implicit type casting exists.
    • Object-orientation: Prototype-based. Objects inherit from objects, not classes.
    • Functions: First-class objects, can be used as constructors, methods, and closures—functions may gather and preserve access to variables from the surrounding environment (even long after their function has executed).
    • Variables: Initially function-scoped(introduced with var), now let/const.
    • Input/Output: Not built-in, but included via libraries within run-time environments.
    • Asynchronous operations: supported using promises and Async/await.
    • Variadic functions: Accept a variable number of arguments (formally via a special arguments object; latterly, the rest operator).
    • Array and object literals: Convenient, concise syntax for creating arrays and objects.
    • Regular Expressions: For powerful text manipulation.
    • Zero-based index: Array and string indexing starts at 0.
    • Modules: JavaScript can now export and import code pieces; modules are a standard way to structure software now.

    JavaScript Execution and Runtimes

    • JavaScript engine: Executes JavaScript code.
    • Modern engines use JIT compilation.
    • Embedded in runtimes (browsers or standalone systems like Node.js).
    • Runtime system provides APIs for I/O tasks (input/output like file access, networking, etc.).
    • Event loop: JavaScript is single-threaded—it processes messages from a queue one at a time (in a non-blocking fashion).

    JavaScript Security

    • Sandboxed execution: Protects against malicious code.
    • Same-origin policy: Limits cross-site access.
    • Cross-site scripting (XSS): Malicious script inserted into a webpage. Solutions include HTML sanitization.
    • Cross-site request forgery (CSRF): Attack where code tricks a user's browser into unwanted actions on a different site. Mitigation requires authentication tokens in forms and headers.

    JavaScript Libraries and Frameworks

    • Client-side scripting is often enhanced using libraries and frameworks.
    • jQuery, Angular, Bootstrap, Lodash, Modernizr, React, Underscore, and Vue are common examples.
    • Vanilla JS signifies use without external libraries.

    JavaScript Beyond Web Browsers

    • JavaScript engines are embedded in various software systems for server-side deployments and non-browser apps.
    • Node.js is a popular runtime system for server-side JavaScript.
    • Frameworks like Electron, Cordova, and React Native use JavaScript for app development.

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    Description

    Explore the essentials of JavaScript, its significance in web development, and its historical background. This quiz covers its programming features, usage in browsers and servers, and the evolution of the language from Netscape Navigator to its current form. Test your knowledge on the key aspects of JavaScript.

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