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JavaScript Fundamentals
Master the core concepts of JavaScript including variables, functions, and scope
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Card 1
What is the difference between let, const, and var in JavaScript?
let and const are block-scoped and cannot be redeclared. var is function-scoped and can be redeclared. const cannot be reassigned after initialization.
Card 2
What is a closure in JavaScript?
A closure is a function that has access to variables in its outer (enclosing) lexical scope, even after the outer function has returned.
Card 3
What is the difference between == and === in JavaScript?
== performs type coercion before comparison, while === (strict equality) compares both value and type without coercion.
Card 4
What is the purpose of the "this" keyword in JavaScript?
"this" refers to the object that is executing the current function. Its value depends on how the function is called.
Card 5
What are arrow functions and how do they differ from regular functions?
Arrow functions have shorter syntax and do not bind their own "this", "arguments", "super", or "new.target". They cannot be used as constructors.
Card 6
What is the event loop in JavaScript?
Card 7
What is the difference between null and undefined?
Card 8
What is a Promise in JavaScript?