🧭 MVC (Model‑View‑Controller) — A Front‑End Deep Dive
Category: general / design-patterns
Difficulty: medium
MVC is a software architectural pattern that separates an application into three interconnected components: Model (data), View (UI), and Controller (logic). This separation of concerns makes code more maintainable, testable, and scalable. 1️⃣ High‑Level Idea [code example] Model = data + business rules View = visual representation (DOM / template) Controller = interprets UI events, updates Model, instructs View to refresh Mental hook: Model is truth, View is paint, Controller is the conductor. 2️⃣ Why Interviewers Love MVC Tests your ability to separate concerns — reduces entangled code. Shows you can explain data flow clearly. Bridges legacy (Backbone) and modern (React, Angular) frameworks. 3️⃣ Concrete Browser Example (Vanilla JS To‑Do List) [code example] [code example] Key take‑aways: View never mutates state directly — only displays. Controller mediates every state change. Model pushes updates via simple pub/sub. 4️⃣ MVC Across Modern Frameworks View Model Backbone.Viewtemplates Backbone.Model / Collection Angular (v2+) Component class (methods) JSX function/component Redux store (reducers) Svelte Component <script>(event handlers) Observation: Modern libraries often collapse View+Controller into a component , pushing state to specialized stores. 5️⃣ Advantages & Trade‑offs ✅ Pros Clear separation of concerns -> easier unit testing. Multiple Views can observe same Model (e.g., list + chart). Scales well when Controllers remain slim (thin glue layer). ⚠️ Cons Boilerplate (three files per feature) in small apps. Risk of Controller bloat — mixing validation, formatting, routing. Harder state trace when Views update Models directly (two‑way binding variants). 6️⃣ Practical Guidelines Keep Models ignorant of UI; they only know plain JS. Controllers are disposable — treat them as wiring; business logic lives in Model. View Logic ≠ Business Logic — no .innerHTML += … inside Models. Use event buses or observer inside Model to notify Views; avoid Views polling. 7️⃣ Typ...