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Understand promises, async/await, event loop, and concurrency
Practice ES6+ features, functional programming, and design patterns
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Closures, scope, and the event loop
Promises, async/await, and callbacks
Prototypes and inheritance
ES6+ features (destructuring, spread, modules)
Functional programming concepts
Design patterns and best practices
A: A closure is when a function retains access to variables from its outer scope even after the outer function has returned. Example: function outer() { let count = 0; return function inner() { return ++count; } }. The inner function has access to 'count' even after outer() finishes executing.
A: The event loop is how JavaScript handles asynchronous operations despite being single-threaded. It continuously checks the call stack and task queues. When the call stack is empty, it takes tasks from the microtask queue (Promises) first, then the macrotask queue (setTimeout, setInterval). This allows non-blocking I/O operations.
A: '===' (strict equality) checks both value and type without coercion. '==' (loose equality) performs type coercion before comparison. Examples: 5 == '5' is true, but 5 === '5' is false. Always prefer === to avoid unexpected behavior from type coercion.
A: 'this' refers to the object executing the current function. In methods, it's the owner object. In regular functions, it's the global object (or undefined in strict mode). Arrow functions don't have their own 'this' - they inherit from parent scope. You can explicitly set 'this' using call(), apply(), or bind().
Understand prototypal inheritance and the prototype chain
Master async/await, Promises, and how to handle errors properly
Know ES6+ features: destructuring, spread/rest operators, template literals
Practice array methods: map, filter, reduce, forEach and when to use each
Understand hoisting, scope (var vs let vs const), and temporal dead zone
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