Javascript Fundamentals

Master 20 core JavaScript concepts with interactive flashcards

What You'll Learn

Master core JavaScript concepts with free interactive flashcards. Learn closures, promises, async/await, DOM, and more. Perfect for beginners and interview prep.

Key Topics

  • Core language features (const, let, var, hoisting)
  • Functions and closures
  • Asynchronous JavaScript (Promises, async/await)
  • Array methods (map, filter, reduce)
  • DOM and event handling

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How to study this deck

Start with a quick skim of the questions, then launch study mode to flip cards until you can answer each prompt without hesitation. Revisit tricky cards using shuffle or reverse order, and schedule a follow-up review within 48 hours to reinforce retention.

Preview: Javascript Fundamentals

Question

What does 'const' declare?

Answer

A constant variable that cannot be reassigned

Question

What is a closure?

Answer

A function that has access to variables in its outer (enclosing) scope

Question

What does 'undefined' mean?

Answer

A variable has been declared but not assigned a value

Question

What is the difference between '==' and '==='?

Answer

'==' checks value equality with type coercion, '===' checks strict equality (value and type)

Question

What is hoisting?

Answer

JavaScript's behavior of moving declarations to the top of their scope before execution

Question

What is the 'this' keyword?

Answer

A reference to the object that is executing the current function

Question

What does 'async/await' do?

Answer

Allows writing asynchronous code in a synchronous-looking manner using Promises

Question

What is the purpose of 'map()'?

Answer

Creates a new array by applying a function to each element of an existing array

Question

What is the DOM?

Answer

Document Object Model - a programming interface for HTML and XML documents

Question

What is event bubbling?

Answer

Events propagate from the target element up through its ancestors in the DOM tree

Question

What is a callback function?

Answer

A function passed as an argument to another function to be executed later

Question

What does 'null' represent?

Answer

An intentional absence of any object value

Question

What is destructuring?

Answer

A syntax for extracting values from arrays or properties from objects into variables

Question

What is the spread operator (...)?

Answer

Expands an iterable (array, object) into individual elements

Question

What is a Promise?

Answer

An object representing the eventual completion or failure of an asynchronous operation

Question

What is the difference between 'let' and 'var'?

Answer

'let' is block-scoped and not hoisted, 'var' is function-scoped and hoisted

Question

What is JSON?

Answer

JavaScript Object Notation - a lightweight data interchange format

Question

What does 'filter()' do?

Answer

Creates a new array with elements that pass a test implemented by a function

Question

What is an arrow function?

Answer

A concise function syntax (=>) that doesn't bind its own 'this'

Question

What is the purpose of 'reduce()'?

Answer

Executes a reducer function on each array element, resulting in a single output value