🚀 Mastering the 10 Pillars of Front-End
Tags: frontend, job, hire, javascript
Published: 2023-09-22 18:03:48


#### Dive into concise explanations, relatable examples, and handy code snippets for every essential concept a senior developer must know! 🔥


---




## 🔄 1. Event Loop

**Explanation:** The event loop checks if the call stack is empty. If so, it checks the message queue for waiting events and executes them.

**Example:** 🍳 Think of a chef (event loop) checking if there's a dish (task) ready. If yes, it's served. If not, they check for new orders (events).

**Code:**
```javascript
console.log('First');
setTimeout(() => {
  console.log('Second');
}, 0);
console.log('Third');  // Outputs: First, Third, Second
```

[📚 Official Resource](https://developer.mozilla.org/en-US/docs/Web/JavaScript/EventLoop)

---

## 🎨 2. Critical Rendering Path

**Explanation:** The steps a browser follows to convert HTML, CSS, and JavaScript into visible pixels.

**Example:** 🏢 Think of constructing a building: foundation (DOM), design (CSSOM), and paint (rendering).

**Official Resource:** [📚 Google Developers - Critical Rendering Path](https://developers.google.com/web/fundamentals/performance/critical-rendering-path)

---

## 🖋️ 3. Let, Const, Var and Block Scoping

**Explanation:** 
- `var`: function-scoped, re-declarable, and updatable.
- `let`: block-scoped, not re-declarable, but updatable.
- `const`: block-scoped, neither re-declarable nor updatable.

**Example:** 🏫 In a classroom: sections (`var`), roll numbers in a section (`let`), and birth names (`const`).

**Code:**
```javascript
var x = 10;
if(true) {
    var x = 20;  
    let y = 30;  
    const z = 40;
}
console.log(x);  // Outputs: 20
```

[📚 Official Resource](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/var)

---

## 🧠 4. Closure

**Explanation:** A function having access to its own variables, outer function's variables, and global variables.

**Example:** 🙋 A person remembering their name, family name, and celebrities' names.

**Code:**
```javascript
function outer() {
  let outerVar = 'Outside!';
  function inner() {
    console.log(outerVar);
  }
  return inner;
}
const myClosure = outer();
myClosure();  // Outputs: Outside!
```

[📚 Official Resource](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Closures)

---

## 🔄 5. Functional Programming

**Explanation:** A paradigm where functions are primary, emphasizing immutability and pure functions.

**Example:** 🥪 Making sandwiches using fresh ingredients and the same recipe.

**Code:**
```javascript
const array = [1, 2, 3];
const double = array.map(item => item * 2);  // [2, 4, 6]
```

[📚 Official Resource](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function)

---

## 🔍 6. This Keyword Behavior

**Explanation:** `this` refers to the object executing the current function. Its context varies.

**Example:** 🎓 In class, `this` student means the one answering.

**Code:**
```javascript
const obj = {
  name: 'John',
  sayName: function() {
    console.log(this.name);
  }
};
obj.sayName();  // Outputs: John
```

[📚 Official Resource](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this)

---

## 🛠️ 7. Frameworks Usage

**Explanation:** Frameworks offer a structure for faster development. Understand their core concepts and the problems they solve.

**Example:** 🚗 Use a car for long distances, not a short walk.

**Official Resource:** Varies, e.g., [📚 React Docs](https://reactjs.org/docs/getting-started.html)

---

## 👩‍👩‍👧 8. Prototypical Inheritance

**Explanation:** In JavaScript, objects inherit properties and methods from others. This is prototypical inheritance.

**Example:** 👪 Children inheriting traits from parents.

**Code:**
```javascript
function Parent() {}
Parent.prototype.sayHello = function() {
  console.log('Hello from parent');
};

function Child() {}
Child.prototype = Object.create(Parent.prototype);
const child = new Child();
child.sayHello();  // Outputs: Hello from parent
```

[📚 Official Resource](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Inheritance_and_the_prototype_chain)

---

## ⌚ 9. Async, Await vs. Promises

**Explanation:** 
- `Promises`: Handle asynchronous operations with states (pending, fulfilled, rejected).
- `async/await`: Makes asynchronous code look synchronous.

**Example:** 📅 Promise is like a task promise. Async/await marks it on a to-do list and waits.

**Code:**
```javascript
// Promise
function fetchData() {
  return new Promise((resolve) => {
    setTimeout(() => {
      resolve('Data fetched');
    }, 2000);
  });
}

// async/await
async function fetchAndDisplay() {
  const data = await fetchData();
  console.log(data);
}
```

[📚 Official Resource](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)

---

## ⏲️ 10. Debounce vs Throttle

**Explanation:** 
- `Debounce`: Groups events if they're in quick succession.
- `Throttle`: Executes a function at most once in a specified period.

**Example:** 🗣️ Debounce waits for someone to finish speaking. Throttle limits speech to once every minute.

**Code:** Using Lodash:
```javascript
// Debounce
const debouncedSave = _.debounce(() => console.log('Saved'), 300);

// Throttle
const throttledSave = _.throttle(() => console.log('Saved'), 300);
```

[📚 Official Resource](https://lodash.com/docs/)

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Best of luck with your interviews! 🍀🚀