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JavaScript language

JavaScript - one of the high level languages (abstractions, garbage collected), interpreted (now JIT-compiled), dynamically/ weakly typed which based on ECMAScript specification

Dynamic typing: Variables can hold any data type without explicit declaration (Types are determined at runtime, Variables can change type)

Weakly typed: Automatic type coercion occurs during operations

Interpreted/JIT compiled: Modern engines use Just-In-Time compilation for performance

Single-threaded: Executes one operation at a time on the main thread

Non-blocking: Asynchronous execution via event loop


Dynamic, weak typed, prototype pattern, prototype inheritance (show diagram and Object.create(null) => no parent prototype example)

Paradigms Supported

  • Object-oriented (prototype-based inheritance)

  • Functional programming (first-class functions, closures, higher-order functions)

  • Imperative programming

  • Event-driven architecture

Modern JavaScript (ES6+)

ES2015 (ES6) Major Features

  • Arrow functions (=>)

  • Classes (syntactic sugar over prototypes)

  • Template literals

  • Destructuring assignment

  • Default parameters

  • Rest/spread operators (...)

  • Promises

  • let/const

  • Modules (import/export)

  • Iterators and generators

Subsequent Additions

  • ES2017: async/await, Object.entries/values

  • ES2018: Rest/spread for objects, async iteration

  • ES2019: Array.flat(), Object.fromEntries()

  • ES2020: Optional chaining (?.), nullish coalescing (??), BigInt

  • ES2021: Logical assignment operators, Promise.any()

  • ES2022: Top-level await, class fields, at() method

  • ES2023: Array methods (toSorted, toReversed), # private fields

Optimization Techniques

  • Minimize DOM manipulation

  • Debounce/throttle event handlers

  • Use Web Workers for heavy computation

  • Lazy loading and code splitting

  • Tree shaking to remove dead code

  • Memoization for expensive operations

Memory Management

  • Automatic garbage collection

  • Avoid memory leaks (closures, event listeners, timers)

  • WeakMap/WeakSet for cache without preventing GC

  • Global variables

Security Concerns

  • XSS (Cross-Site Scripting): Sanitize user input

  • CSRF (Cross-Site Request Forgery): Use tokens

  • Code injection: Avoid eval(), careful with innerHTML

  • Dependency vulnerabilities: Regular audits (npm audit)

  • Prototype pollution: Validate object property access

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