JavaScript

Use let and const for block-scoped variable declarations in JavaScript. let allows reassignment, while const creates an immutable binding for variables that should not be reassigned.

The difference between var, let, and const in JavaScript is that var is function-scoped, while let and const are block-scoped. const additionally prevents variable reassignment after initialization.

Promises and async/await handle asynchronous programming in JavaScript by allowing code to pause execution until operations complete. async/await provides syntax built on Promises to write asynchronous code sequentially.

Use ES6 features like arrow functions and destructuring in JavaScript to write concise syntax. Arrow functions bind the lexical this context, while destructuring unpacks values from arrays or objects into distinct variables.

Closures in JavaScript functions occur when an inner function retains access to its outer function's scope. This mechanism allows data encapsulation and state persistence after the outer function executes.

Use the this keyword in JavaScript objects to reference the current execution context, and use prototypes to share methods across object instances. Constructors initialize objects, setting up properties for inheritance.