JavaScript Overview and Web Standards
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Questions and Answers

What is the primary purpose of web standards?

  • To enable websites to be developed in one specific programming language
  • To limit the use of scripting languages on websites
  • To ensure consistent functionality across different browsers and devices (correct)
  • To create websites that work on a single platform

Which organization is known for creating standards for the World Wide Web?

  • ECMAScript Association
  • Open Web Application Security Project (OWASP)
  • World Wide Web Consortium (W3C) (correct)
  • Internet Engineering Task Force (IETF)

What does the concept of Just-in-Time (JIT) compilation refer to?

  • Compiling code during runtime for optimization (correct)
  • Interpreting code line by line during execution
  • Transpiling code from one language to another before execution
  • Compiling source code before the program runs

Which one of these is NOT an example of a language that transpiles to JavaScript?

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

What role does the JavaScript Engine play in executing JavaScript code?

<p>It executes JavaScript code in the browser environment (D)</p> Signup and view all the answers

Which of the following statements about ECMAScript is true?

<p>It is the standard that defines scripting languages like JavaScript (D)</p> Signup and view all the answers

Which JavaScript Engine is known to be the most popular?

<p>Google’s V8 Engine (D)</p> Signup and view all the answers

What does transpilation allow developers to do?

<p>Use an alternate programming language that compiles to JavaScript (B)</p> Signup and view all the answers

What is the primary purpose of WebAssembly?

<p>To speed up code execution inside web browsers. (A)</p> Signup and view all the answers

Which keyword is recommended for use as much as possible when declaring variables in JavaScript?

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

What defines the accessibility of a variable within JavaScript code?

<p>The variable's scope. (C)</p> Signup and view all the answers

Which scope allows variables to be accessed from anywhere in the code?

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

How do the variable declarations differ between 'var' and 'let' in JavaScript?

<p>'var' is hoisted while 'let' is not hoisted. (D)</p> Signup and view all the answers

Which keyword allows variable declarations that cannot be reassigned after their initial value?

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

What does hoisting in JavaScript refer to?

<p>Variable and function declarations being moved to the top of their scope before execution. (B)</p> Signup and view all the answers

What is true about block scope in JavaScript?

<p>Variables declared within a block are only accessible within that block. (D)</p> Signup and view all the answers

What is a key feature of JavaScript objects?

<p>Keys must be of type string, while values can be of any type. (A)</p> Signup and view all the answers

How can you incorporate expressions within strings in JavaScript?

<p>By using template literals enclosed in backticks. (B)</p> Signup and view all the answers

What distinguishes a function declaration from a function expression in JavaScript?

<p>Function declarations are hoisted, while function expressions are not. (C)</p> Signup and view all the answers

What is the purpose of an Immediately Invoked Function Expression (IIFE)?

<p>To execute a function immediately after its creation. (B)</p> Signup and view all the answers

What is true about named functions in JavaScript?

<p>They provide better debugging insights compared to anonymous functions. (C)</p> Signup and view all the answers

Which statement about template literals is incorrect?

<p>They cannot include embedded expressions. (A)</p> Signup and view all the answers

In a function expression, what characteristic is true?

<p>They can be anonymous or named but are not hoisted. (C)</p> Signup and view all the answers

What is a correct way to declare an Immediately Invoked Function Expression (IIFE)?

<p>(function() { console.log('Hello'); })(); (B)</p> Signup and view all the answers

Flashcards

Web Standards

A set of formal guidelines and technical specifications that ensure websites and web technologies work consistently across different browsers, devices, and platforms. They are created by standards bodies like the W3C.

W3C

The best known web standards body, primarily focusing on HTML, CSS, and other web technologies.

JavaScript

A scripting language initially designed for web page interactions, now used extensively on the server-side (Node.js) and mobile devices (React Native).

ECMAScript

The core features of JavaScript are based on this standard.

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JavaScript Engine

The software component that executes JavaScript code. All modern browsers have them. Google's V8 Engine is a prime example.

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Just-in-Time (JIT) Compilation

A technique for speeding up code execution by compiling it during runtime. It helps make JavaScript faster.

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JavaScript Alternatives

Languages that are translated into JavaScript before being executed by the browser. This allows developers to code in other languages and streamline the process.

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JavaScript (JS)

A language that is used to add interactivity to websites. It is known for its versatility and popularity.

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JavaScript Objects

A collection of key-value pairs where keys are always strings and values can be various data types like strings, numbers, arrays, or even functions.

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JavaScript Template Literals

A syntax that allows embedding expressions within strings using backticks (`). It supports single and double quotes within the string and allows for multi-line strings.

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Function Declaration (JavaScript)

A function declaration defines a named function before the execution of the code. This means that the function can be used before its declaration in the code.

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Function Expression (JavaScript)

A function expression defines a function as part of an expression, usually assigned to a variable. It cannot be used before its declaration.

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Immediately Invoked Function Expression (IIFE)

An anonymous function expression that immediately executes itself after being defined. Often used to create self-contained code blocks.

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Variable Scope (JavaScript)

A variable's scope refers to the region of code where it is accessible. It determines which parts of the program can use a particular variable.

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What is WebAssembly (WASM)?

WebAssembly is a language that runs in web browsers for faster code execution. It's like a translator for code written in other languages.

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What is Variable Scope?

The scope of a variable determines its visibility - which parts of the code can access and use it.

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How does Variable Scope work?

A variable's scope determines from where within the code you can use it.

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What are the different ways to declare variables in JavaScript?

JavaScript offers three keywords for variable declarations: var, let, and const. They differ in scope, hoisting, and reassignment.

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What is global scope in JavaScript?

Variables declared outside any function or block belong to the global scope, making them accessible from anywhere in the code.

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What is function scope in JavaScript?

Variables declared within a function can only be accessed within that function. Their scope is limited to that specific function.

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What is block scope in JavaScript?

Variables declared within a block (inside curly braces {}) are only accessible within that block. They're confined to the specific block of code.

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What is Hoisting in JavaScript?

Hoisting in JavaScript means that variable and function declarations are moved to the top of their scope before execution. The declaration is hoisted, but not the initialization.

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Study Notes

JavaScript Overview

  • JavaScript is a scripting language used for web pages
  • It interacts with web page elements allowing dynamic content and functionality
  • JavaScript code can be embedded directly within HTML
  • JavaScript is used for server-side development (Node.js) and mobile applications (React Native)

Web Standards

  • Web standards are formal guidelines and technical specifications
  • Created by standards bodies to ensure consistent web technology across browsers, devices, and platforms
  • W3C is the primary web standards body
  • ECMAScript (ECMA-262) is a standard for scripting languages, including JavaScript

JavaScript Engine

  • JavaScript's core functions are based on the ECMAScript standard
  • Execution is handled by the JavaScript Engine
  • Modern browsers contain their own JavaScript Engine versions
  • Google's V8 Engine is a widely used, created in 2008
  • Current engines use Just-in-Time (JIT) compilation, combining compilation and interpretation for optimized performance

Interpretation vs Compilation

  • JIT compilation compiles code during runtime instead of before program execution
  • A monitor (profiler) is added to track code behavior and optimize it dynamically

JavaScript Engine Structure

  • Source code is parsed into an Abstract Syntax Tree
  • Interpreted into bytecode
  • Optimized by an optimizing compiler
  • Dynamic optimization is employed for optimized code execution

JavaScript Alternatives

  • Some languages are transpiled (converted) into JavaScript before running in the browser, speeding up code execution
  • Modern tools make transpilation fast and transparent
  • Examples of such languages include TypeScript, Dart, Brython, and Kotlin

WebAssembly

  • WebAssembly (WASM) is a fourth language, besides HTML, CSS, and JavaScript, for web browsers execution, improving performance
  • Originally created to speed up code execution within web browsers
  • Developers write in other languages and compile to WASM bytecode
  • Bytecode runs on web browsers, translating it to native machine code for high-speed execution

Variable Scope

  • Scope manages variable accessibility
  • Variables' scope defines the area within code where a variable can be used
  • JavaScript has different variable scopes (global, function, block)

JavaScript Variable Keywords

  • JavaScript uses var, let, and const to declare variables
  • const is preferred for variables not requiring reassignment
  • let is used for variables that might change

Variable Scope: Global

  • Variables declared outside functions or blocks are accessible throughout the code

Variable Scope: Function

  • Variables declared within functions are only accessible within that function

Variable Scope: Block

  • Variables declared inside curly braces are only accessible within that specific block.
  • Variables declared with const cannot be reassigned after initial assignment
  • Contents of objects/arrays declared by const can be modified

Hoisting

  • Hoisting in JavaScript moves variable and function declarations to the top of their scopes before execution
  • Only declarations are hoisted, not initializations

JavaScript Objects

  • Objects are collections of key-value pairs in JavaScript
  • Keys are strings
  • Values can be any valid JavaScript type, including functions, numbers, arrays, etc

Template Literals

  • Template literals use backticks (` ``) to define strings
  • Allow embedded expressions within strings
  • Support multiline strings

Function Declaration

  • Function declarations define named functions
  • Hoisted to the top of their scope
  • Can be used before they're declared

Function Expressions

  • Function expressions define anonymous functions as part of an expression
  • Usually assigned to a variable
  • Not hoisted; cannot be invoked before definition

Immediately Invoked Function Expressions (IIFE)

  • Anonymous functions that invoke themselves upon creation
  • Use parentheses () to indicate their function nature

Arrow Functions

  • Concise function syntax using => instead of function

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JavaScript Concepts PDF

Description

Explore the fundamentals of JavaScript, a crucial scripting language for web development. This quiz covers its interaction with web elements, web standards set by W3C, and the role of JavaScript engines like Google's V8. Test your knowledge and understanding of these key concepts in modern web technology.

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