JavaScript Fundamentals and Web Standards
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Questions and Answers

What does WebAssembly allow developers to do?

  • Automate CSS styling.
  • Create dynamic HTML without JavaScript.
  • Run code in the browser at high speed. (correct)
  • Write code directly in WebAssembly.

    • Which of the following correctly describes variable scope?

  • Scope is only relevant for global variables.
  • Scope refers to the data type of variables.
  • Scope determines where a variable can be accessed in code. (correct)
  • Scope restricts variables to function declarations only.

    • Which keyword should generally be avoided in modern JavaScript code?

  • const
  • var (correct)
  • function
  • let

    • What type of scope do variables declared outside of any function or block have?

    <p>Global Scope</p> Signup and view all the answers

    Which statement about const variables is true?

    <p>They cannot be reassigned after creation.</p> Signup and view all the answers

    What is hoisting in JavaScript?

    <p>Moving variable and function declarations to the top of their scope.</p> Signup and view all the answers

    In which scope are variables declared with let or const confined?

    <p>Block Scope only.</p> Signup and view all the answers

    What does the scope policy manage?

    <p>The visibility and accessibility of variables.</p> Signup and view all the answers

    What is the primary purpose of web standards?

    <p>To ensure consistent functionality across different platforms</p> Signup and view all the answers

    Which of the following scripting languages is standardized by ECMAScript (ECMA-262)?

    <p>JavaScript</p> Signup and view all the answers

    What concept does the JavaScript engine primarily rely on for executing code?

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

    What is the role of the monitor (profiler) in JIT compilation?

    <p>To optimize code during runtime based on performance</p> Signup and view all the answers

    Which of the following languages is NOT mentioned as a transpiled alternative to JavaScript?

    <p>CoffeeScript</p> Signup and view all the answers

    What is a significant benefit of modern transpilation tools?

    <p>They make transpilation fast and transparent for developers</p> Signup and view all the answers

    Which JavaScript engine is recognized as one of the most popular?

    <p>Google's V8 Engine</p> Signup and view all the answers

    What functionality does JavaScript primarily provide for web pages?

    <p>Interaction with HTML elements</p> Signup and view all the answers

    What is the primary characteristic of a JavaScript object?

    <p>It consists of key-value pairs.</p> Signup and view all the answers

    What are template literals in JavaScript used for?

    <p>Using embedded expressions within strings.</p> Signup and view all the answers

    Which statement correctly describes a function declaration in JavaScript?

    <p>It is hoisted to the top of its scope.</p> Signup and view all the answers

    What is the key difference between a function declaration and a function expression?

    <p>Function expressions can only be used after they are defined.</p> Signup and view all the answers

    What does IIFE stand for in JavaScript?

    <p>Immediately Invoked Function Expression</p> Signup and view all the answers

    What is a requirement for an IIFE in JavaScript?

    <p>It must be followed by parentheses.</p> Signup and view all the answers

    Which of the following is NOT a characteristic of a function expression?

    <p>It is hoisted within its scope.</p> Signup and view all the answers

    What type of keys can a JavaScript object have?

    <p>Only string keys.</p> Signup and view all the answers

    Study Notes

    JavaScript Fundamentals

    • JavaScript is a scripting language used to interact with web page elements.
    • JavaScript programs, called scripts, can be embedded within HTML and run automatically when the page loads.
    • JavaScript is now used for server-side development (Node.js) and mobile app development (React Native).

    Web Standards

    • Web standards are formal guidelines and technical specifications created by standard bodies.
    • These standards ensure websites and web technologies function consistently across different browsers, devices, and platforms.
    • The W3C (World Wide Web Consortium) is a well-known body that establishes standards for the World Wide Web (HTML, CSS, etc.).
    • ECMAScript (ECMA-262) defines the standard for scripting languages, including JavaScript, JScript, and others.

    JavaScript Engine

    • JavaScript's core functionality is based on the ECMAScript standard.
    • JavaScript code execution is handled by a JavaScript engine.
    • Modern browsers include a JavaScript engine, with Google's V8 engine being one of the most popular options (developed in 2008).
    • Modern JavaScript engines utilize JIT (Just-in-Time) compilation, combining compilation and interpretation during runtime.

    Interpretation vs. Compilation

    • JIT compilation compiles code during runtime rather than beforehand.
    • A monitor (profiler) is added to track code behavior during execution, enabling optimizations.

    JavaScript Engine Architecture (Conceptual)

    • JavaScript source code is parsed.
    • The abstract syntax tree is built.
    • Interpreted bytecode is generated and optimized.
    • Optimized code is delivered.

    JavaScript Alternatives

    • New languages are transpiled into JavaScript before running in the browser to enhance development with modern tools.
    • Examples include TypeScript (developed by Microsoft), Dart (developed by Google), Brython and Kotlin..etc.

    WebAssembly

    • Besides HTML, CSS, and JavaScript, WebAssembly is a language supported by W3C, facilitating code execution within the browser.
    • WebAssembly (WASM) was created to enhance code execution speed within web browsers.
    • Developers write code in languages of their choice, which are compiled into WebAssembly bytecode.
    • Bytecode is run within the web browser, translated into machine code, and executed.

    Variable Scope

    • Scope is a policy regulating variable accessibility in code.
    • A variable's scope defines the portion of code where the variable can be used.
    • JavaScript variables are declared using keywords like var, let, and const.

    Variable Scope (Types)

    • Global Scope: Variables declared outside functions are accessible anywhere in the code.
    • Function Scope: Variables declared within a function are accessible only within that function.
    • Block Scope: Variables declared within a block (curly braces) are accessible only within that block (introduced with let and const).

    Hoisting

    • Hoisting in JavaScript involves moving variable and function declarations to the top of their scope before code execution.
    • Only declarations are hoisted, not initializations. This means you can reference a variable before its initialization in the code due to hoisting.

    Objects

    • JavaScript objects are collections of key-value pairs.
    • Object keys are strings while values can be any data type (e.g., numbers, arrays, and functions.)

    Template Literals

    • Template literals (backticks) enable use of strings or embedded expressions.
    • They support embedded expressions in strings using the ${expression} syntax.
    • Template literals allow multiline strings and single/double quotes within the string.

    Function Declaration

    • Function declarations define named functionalities, are hoisted.
    • Can be used before their declaration.

    Function Expression

    • Function expressions define functions as part of an expression, often assigned to a variable.
    • Not hoisted; usable only after definition.
    • Function expressions can be anonymous (without a name) or named.

    Immediately Invoked Function Expression (IIFE)

    • IIFE is a way to execute an anonymous function immediately upon creation.
    • An IIFE is encapsulated with parentheses.
    • Executed immediately, potentially for limited scope or privacy concerns.

    Arrow Functions

    • Arrow functions are a concise and alternative way to create functions in JavaScript.

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    JavaScript Concepts PDF

    Description

    Explore the essential concepts of JavaScript, including its role as a scripting language and its integration with HTML. Learn about web standards set by bodies like W3C and how they ensure consistent web functionality. Additionally, understand the significance of the ECMAScript standard in JavaScript engine operations.

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