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

Which statement about const variables is true?

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

What is hoisting in JavaScript?

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

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

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

What does the scope policy manage?

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

What is the primary purpose of web standards?

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

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

<p>JavaScript (A)</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 (D)</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 (C)</p> Signup and view all the answers

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

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

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

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

What functionality does JavaScript primarily provide for web pages?

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

What is the primary characteristic of a JavaScript object?

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

What are template literals in JavaScript used for?

<p>Using embedded expressions within strings. (B)</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. (A)</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. (C)</p> Signup and view all the answers

What does IIFE stand for in JavaScript?

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

What is a requirement for an IIFE in JavaScript?

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

What type of keys can a JavaScript object have?

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

Flashcards

Web Standards

Formal guidelines and technical specifications created by standards bodies that ensure websites and web technologies work consistently across different browsers, devices, and platforms.

JavaScript

A scripting language largely used for web pages, but also in server-side development and mobile devices.

ECMAScript

The standard for scripting languages, including JavaScript.

JavaScript Engine

The software that executes JavaScript code, typically built into web browsers.

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Just-In-Time (JIT) Compilation

A technique where code is compiled during runtime, making JavaScript faster by optimizing code as it runs.

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Transpilation

A process of converting code written in one language (like TypeScript) into another language (like JavaScript) that can be executed by the browser.

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TypeScript

Developed by Microsoft, a language that gets transpiled into JavaScript.

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Dart

Developed by Google, a language that gets transpiled into JavaScript.

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What is WebAssembly?

WebAssembly (WASM) is a binary instruction format designed to run code in web browsers at near-native speeds. It is the fourth language, alongside HTML, CSS, and JavaScript, officially supported by the World Wide Web Consortium (W3C).

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How is WebAssembly used?

Developers do not write WebAssembly directly. Instead, they write code in their preferred language (e.g., C++, Python, Rust), which is then compiled into WebAssembly bytecode. This bytecode is executed within web browsers, where it's translated into native machine code for efficient performance.

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What is variable scope in JavaScript?

Scope in JavaScript defines the accessibility of variables within different parts of the code. It determines from where within the program a variable can be accessed.

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What is global scope in JavaScript?

Variables declared outside of any function or code block are in the global scope. This means they can be accessed from anywhere within the program.

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What is function scope in JavaScript?

Variables declared within a function are only accessible within that specific function. They are not visible or usable outside of it.

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What is block scope in JavaScript?

Variables declared within a block (code enclosed in curly braces { } ) are only accessible within that block. They are not visible outside of it.

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What are variables declared with 'const' in JavaScript?

The 'const' keyword in JavaScript prevents variables from being reassigned after their initial value is set. You can still modify the content of objects or arrays declared with 'const'.

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What is hoisting in JavaScript?

In JavaScript, hoisting refers to the process where variable and function declarations are moved to the top of their scope before code execution. Only the declaration is hoisted, not the initialization.

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What is an object in JavaScript?

An object in JavaScript is a collection of key-value pairs. The keys must be strings, and the values can be of any type, including strings, numbers, arrays, and even functions.

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What are template literals in JavaScript?

A template literal lets you embed expressions within a string enclosed by backticks (`). This allows you to use single and double quotes within the string, and even create multiline strings.

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What is a function declaration in JavaScript?

Function declaration defines a function with a name and is hoisted to the top of its scope. This means you can use the function before it's declared in the code.

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What is a function expression in JavaScript?

A function expression defines a function as part of an expression, often assigned to a variable. It's not hoisted, meaning you can only use it after it's defined in the code.

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What is an IIFE in JavaScript?

An IIFE (Immediately Invoked Function Expression) allows you to create an anonymous function that executes immediately upon creation. You create an anonymous function and then immediately call it, often used to isolate scope and avoid polluting global namespace.

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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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Related Documents

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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