Explain JS event loop and related concepts

You are interviewing for a frontend JavaScript position. Answer the following conceptual and practical questions. ### 1. JavaScript Event Loop, Microtasks, and Macrotasks Explain how the JavaScript event loop works in a browser environment. - What is the **call stack**? - What is the **event loop**? - What are **macrotasks** (also called tasks)? Give common examples (e.g., `setTimeout`, `setInterval`, DOM events, etc.). - What are **microtasks**? Give common examples (e.g., `Promise.then`, `MutationObserver`, etc.). - In what order are microtasks and macrotasks executed relative to each other and to rendering/painting? Describe a typical sequence for one event loop tick. ### 2. Difference Between `var` and `let` Explain the differences between `var` and `let` in JavaScript, focusing on: - Scope (function scope vs block scope). - Hoisting behavior. - The "temporal dead zone". - Re-declaration rules. - How they behave when declared in the global scope (relationship to the global object). Optionally, briefly contrast `const` with `let` as well. ### 3. `this` Binding in JavaScript Explain how the value of `this` is determined in the following contexts: - In the global scope. - Inside a regular function call (not attached to an object). - Inside a method call on an object. - Inside an event handler in the browser. - Inside an arrow function. Then describe at least **three different ways** to explicitly control or fix the value of `this` (for example, with `bind`, `call`, `apply`, storing `this` in another variable, using arrow functions, etc.), and give short code examples. ### 4. Draw a 2x2 Square Grid with HTML and CSS Using only HTML and CSS (no JavaScript), write markup and styles to draw a **square** that is divided into **four equal smaller squares** (a 2x2 grid), each with visible borders. - Assume the outer square should be, for example, **200px by 200px**. - The 4 inner squares should be equal in size and fill the outer square exactly. - Use any reasonable CSS layout technique (e.g., flexbox, CSS grid, or percentage-based widths/heights). Provide the HTML and CSS code required.