Podcast
Questions and Answers
What is the primary purpose of web standards?
What is the primary purpose of web standards?
Which organization is best known for creating web standards for the World Wide Web?
Which organization is best known for creating web standards for the World Wide Web?
Which of the following statements about JavaScript is true?
Which of the following statements about JavaScript is true?
What does the JavaScript Engine primarily do?
What does the JavaScript Engine primarily do?
Signup and view all the answers
What is the concept used by modern JavaScript Engines that combines both compilation and interpretation?
What is the concept used by modern JavaScript Engines that combines both compilation and interpretation?
Signup and view all the answers
Which JavaScript alternative is developed by Microsoft?
Which JavaScript alternative is developed by Microsoft?
Signup and view all the answers
How does JIT compilation optimize code during its execution?
How does JIT compilation optimize code during its execution?
Signup and view all the answers
What is the role of transpilation in modern web development?
What is the role of transpilation in modern web development?
Signup and view all the answers
What is a key characteristic of objects in JavaScript?
What is a key characteristic of objects in JavaScript?
Signup and view all the answers
What feature do template literals provide in JavaScript?
What feature do template literals provide in JavaScript?
Signup and view all the answers
Which statement is true regarding function declarations in JavaScript?
Which statement is true regarding function declarations in JavaScript?
Signup and view all the answers
What is a distinctive feature of function expressions?
What is a distinctive feature of function expressions?
Signup and view all the answers
What occurs when an Immediately Invoked Function Expression (IIFE) is created?
What occurs when an Immediately Invoked Function Expression (IIFE) is created?
Signup and view all the answers
Which of the following is NOT a valid use case for template literals?
Which of the following is NOT a valid use case for template literals?
Signup and view all the answers
Which statement about function expressions is correct?
Which statement about function expressions is correct?
Signup and view all the answers
How should you format an IIFE in JavaScript?
How should you format an IIFE in JavaScript?
Signup and view all the answers
What is the main purpose of WebAssembly?
What is the main purpose of WebAssembly?
Signup and view all the answers
Which keyword should generally be avoided outside of legacy code in JavaScript?
Which keyword should generally be avoided outside of legacy code in JavaScript?
Signup and view all the answers
What type of scope allows variables to be accessed from anywhere in the code?
What type of scope allows variables to be accessed from anywhere in the code?
Signup and view all the answers
What does hoisting refer to in JavaScript?
What does hoisting refer to in JavaScript?
Signup and view all the answers
Which of the following scopes is limited to variables declared within curly braces?
Which of the following scopes is limited to variables declared within curly braces?
Signup and view all the answers
What occurs when a variable declared with 'const' is assigned a new value?
What occurs when a variable declared with 'const' is assigned a new value?
Signup and view all the answers
Which JavaScript keyword should be used for loop counters when reassigning values?
Which JavaScript keyword should be used for loop counters when reassigning values?
Signup and view all the answers
Which of the following describes a variable's scope?
Which of the following describes a variable's scope?
Signup and view all the answers
Study Notes
JavaScript Overview
- JavaScript is a scripting language used to interact with web page elements.
- JavaScript programs are called scripts, written directly in a web page's HTML.
- Scripts run automatically when a web page loads.
- JavaScript is used in server-side developments (Node.js) and mobile devices (React Native).
Web Standards
- Web standards are formal guidelines and technical specifications created by standard bodies (e.g., W3C).
- They ensure websites and web technologies work consistently across various browsers, devices, and platforms.
- W3C is a well-known web standards body, creating standards for the World Wide Web (HTML, CSS, etc.).
- ECMAScript (ECMA-262) is a standard for scripting languages, including JavaScript, JScript, and ActionScript.
JavaScript Engine
- JavaScript's core features are based on the ECMAScript standard.
- JavaScript code execution is handled by a JavaScript Engine.
- Modern browsers have their own JavaScript Engines, with Google's V8 Engine being a popular choice (created in 2008).
- Current JavaScript Engines use Just-in-Time (JIT) compilation, combining compilation and interpretation during runtime.
Interpretation vs. Compilation
- JIT Compilation: Code compiles during runtime, not before, for faster program execution.
- This technique uses a monitor (profiler) to track code behavior and optimize its performance.
JavaScript Engine Architecture
- JavaScript source code is parsed (transformed into an Abstract Syntax Tree).
- The interpreter translates the bytecode into optimized code, which is then executed.
JavaScript Alternatives
- Emerging languages are transpiled into JavaScript before running in browsers.
- Tools perform fast and transparent transpilation, allowing developers to write code in other languages and automatically convert it.
- Examples: TypeScript (Microsoft), Dart (Google), Brython, Kotlin, etc.
WebAssembly
- WebAssembly (WASM) is a new language for the web, in addition to HTML, CSS, and JavaScript, that enables faster execution.
- It uses a bytecode that gets translated to native machine code for high-speed execution.
- Developers write in other languages and compile into WebAssembly bytecode which runs in the browser.
Variable Scope
- Scope manages variable accessibility.
- A variable's scope determines from where the code can access it.
- Global scope: Variables declared outside functions are accessible anywhere in the code.
- Function scope: Variables declared within a function are only accessible within that function.
- Block scope (let and const): Variables declared within a block (curly braces) are accessible only within that block.
-
constvariables cannot be reassigned after initialization.
-
Hoisting
- Hoisting in JavaScript moves variable and function declarations to the top of their scope before code execution.
- Only declarations are hoisted, not initializations.
Objects
- JavaScript objects are collections of key-value pairs.
- Property keys are strings, values can be anything (strings, numbers, arrays, or functions).
JavaScript Template Literals
- Template literals are strings enabling embedded expressions. They use backticks (
...). - They allow single and double quotes within strings.
- They support multiline strings and expressions within the strings.
Function Declaration
- Function declaration defines a named function.
- Functions are hoisted to the top of their scope, and usable before they are declared.
Function Expression
- Function expression defines a function as part of an expression, often assigned to a variable.
- Functions are not hoisted, they can only be used after they are defined.
Immediately Invoked Function Expression (IIFE)
- IIFEs are anonymous functions that execute immediately upon their creation.
Arrow Functions
- Arrow functions are a concise way to define functions in JavaScript.
- They use an arrow
=>instead of thefunctionkeyword.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Explore the fundamentals of JavaScript, including its role as a scripting language for web pages and server-side development. Understand key web standards established by bodies like W3C and the importance of ECMAScript. Dive into how JavaScript engines execute code in modern browsers.
