In learning JavaScript, you must understand some basic knowledge, such as variables, functions, classes, loops, etc. These basics are the basis for our use of JavaScript . However, in daily business development, we need some more advanced skills to better solve problems.
By reading this article, you will learn advanced knowledge points and practical application skills of JS, such as advanced data structures and algorithms, functional programming, asynchronous programming and object-oriented programming. I will use code examples to help everyone better understand these knowledge points. At the same time, I will also provide some practical case demonstrations and usage techniques, so that you can better apply these technologies.
Advanced Data Structures and Algorithms
Map and Set Data Structures
The Map data structure is usually used to store key-value pairs, which can use arbitrary types as keys and values. Set data structure is used to store a collection of unique values.
// Create a Map object
const map = new Map();
// Set key-value pairs
map.set('name', 'Tom');
map.set('age', 20);
// Get key-value pairs
console.log(map.get('name')); // 'Tom'
console.log(map.get('age')); // 20
// Create a Set object
const set = new Set();
// Add elements
set.add(10);
set.add(20);
set.add(30);
// Remove elements
set.delete(20);
// Check if an element exists
console.log(set.has(10)); // true
console.log(set.has(20)); // false
Heap, Stack and Queue
Heap and stack are commonly used memory allocation methods. The stack is a last-in, first-out (LIFO) data structure, and the heap is a dynamically allocated memory structure. A queue is a first-in, first-out (FIFO) data structure that is commonly used in caching and concurrent programming.
// Simulate a heap using an array
const arr = [1, 2, 3, 4];
arr.push(5); // Push to the heap
console.log(arr.pop()); // Pop from the heap
// Simulate a stack using an array
const stack = [1, 2, 3, 4];
stack.push(5); // Push to the stack
console.log(stack.pop()); // Pop from the stack
// Simulate a queue using an array
const queue = [1, 2, 3, 4];
queue.push(5); // Push to the queue
console.log(queue.shift()); // Pop from the queue
Depth-first Search and Breadth-first Search
Depth-first search (DFS) and breadth-first search (BFS) are commonly used graph traversal algorithms. DFS is typically used to solve depth-first problems, while BFS is suitable for breadth-first problems.
// Depth-first traversal
function dfs(node) {
if (node === null) return;
console.log(node.value); // Print the value of the node
dfs(node.left); // Recursively traverse the left subtree
dfs(node.right); // Recursively traverse the right subtree
}
// Breadth-first traversal
function bfs(node) {
const queue = [node]; // Create a queue and enqueue the root node
while (queue.length) {
const curr = queue.shift(); // Dequeue the first node from the queue
console.log(curr.value); // Print the value of the node
if (curr.left) queue.push(curr.left); // Enqueue the left child of the node
if (curr.right) queue.push(curr.right); // Enqueue the right child of the node
}
}
Commonly Used Algorithms
Commonly used algorithms include sorting, search, and lookup.
Sorting Algorithm: Quick Sort uses the idea of divide and conquer, sorting by dividing the array into smaller blocks.
function quickSort(arr) {
if (arr.length < 2) {
return arr;
}
let pivot = arr[0];
let left = [];
let right = [];
for (let i = 1; i < arr.length; i++) {
if (arr[i] < pivot) {
left.push(arr[i]);
} else {
right.push(arr[i]);
}
}
return [...quickSort(left), pivot, ...quickSort(right)];
}
// Search algorithm：
function binarySearch(arr, target) {
let left = 0;
let right = arr.length - 1;
while (left <= right) {
const mid = Math.floor((left + right) / 2);
if (arr[mid] === target) {
return mid;
} else if (arr[mid] < target) {
left = mid + 1;
} else {
right = mid - 1;
}
}
return -1;
}
Functional Programming
Higher-order Functions and Currying
Higher-order functions and currying are common concepts in functional programming that allow us to create more abstract and flexible functions.
// Higher order function
function higherOrderFunction(func) {
return function (num) {
return func(num);
};
}
function double(num) {
return num * 2;
}
const doubleFunc = higherOrderFunction(double);
console.log(doubleFunc(10)); // 20
// Currying
function curry(func) {
return function curried(...args) {
if (args.length >= func.length) {
return func.apply(this, args);
} else {
return function (...args2) {
return curried.apply(this, [...args, ...args2]);
};
}
};
}
function sum(a, b, c) {
return a + b + c;
}
const curriedSum = curry(sum);
console.log(curriedSum(1)(2)(3)); // 6
Closures and Scope
Closures and scope are relatively common concepts in JavaScript . Closures allow us to maintain state within a function, and scope determines the visible range of variables.
// Closure
function closure() {
let i = 0;
return function () {
return ++i;
};
}
const func = closure();
console.log(func()); // 1
console.log(func()); // 2
// Scope
let a = 10;
function foo() {
let a = 20;
console.log(a); // 20
}
foo();
console.log(a); // 10
Common Patterns in Functional Programming
There are many common patterns in functional programming, such as map, filter, and reduce.
// map
const arr = [1, 2, 3];
const mapArr = arr.map((item) => item * 2);
console.log(mapArr); // [2, 4, 6]
// filter
const filterArr = arr.filter((item) => item > 1);
console.log(filterArr); // [2, 3]
// reduce
const reduceArr = arr.reduce((sum, curr) => sum + curr, 0);
console.log(reduceArr); // 6
Asynchronous Programming
Promise and async/await
Promise and async/await are common asynchronous programming methods, which allow us to better deal with problems in asynchronous programming.
// Promise
function promise() {
return new Promise((resolve, reject) => {
setTimeout(() => {
resolve('done');
}, 1000);
});
}
promise().then((result) => console.log(result)); // 'done'
// async/await
async function asyncFunc() {
const result = await promise();
console.log(result);
}
asyncFunc(); // 'done'
Event loop and EventEmitter
// Event loop
console.log('start');
setTimeout(() => {
console.log('setTimeout');
}, 0);
Promise.resolve().then(() => console.log('promise'));
console.log('end');
// EventEmitter
const { EventEmitter } = require('events');
const emitter = new EventEmitter();
emitter.on('doSomething', (arg1, arg2) => {
console.log(`${arg1} ${arg2}`);
});
emitter.emit('doSomething', 'Hello', 'World'); // 'Hello World'
Web Worker
Web Workers allow us to move long-running tasks off the main thread to avoid blocking the UI.
// main thread
const worker = new Worker('worker.js');
worker.onmessage = (event) => {
console.log(event.data);
};
worker.postMessage('start');
// worker.js
self.onmessage = (event) => {
const result = longCalculation(event.data);
self.postMessage(result);
};
Object Oriented Programming
Classes and inheritance
Classes and inheritance in JavaScript are similar to other object-oriented programming languages.
class Animal {
constructor(name) {
this.name = name;
}
speak() {
console.log(`${this.name} makes a noise.`);
}
}
class Cat extends Animal {
constructor(name, breed) {
super(name);
this.breed = breed;
}
speak() {
console.log(`${this.name} meows.`);
}
get description() {
return `${this.name} is a ${this.breed} cat.`;
}
set nickname(nick) {
this.name = nick;
}
}
const cat = new Cat('Fluffy', 'Persian');
cat.speak(); // 'Fluffy meows.'
console.log(cat.description); // 'Fluffy is a Persian cat.'
cat.nickname = 'Fuffy';
console.log(cat.name); // 'Fuffy'
Encapsulation, Inheritance, Polymorphism
Encapsulation, inheritance, and polymorphism are important concepts in object-oriented programming.
// Encapsulation
class Person {
constructor(name) {
this._name = name;
}
get name() {
return this._name.toUpperCase();
}
set name(newName) {
this._name = newName;
}
}
const person = new Person('John');
console.log(person.name); // 'JOHN'
person.name = 'Lisa';
console.log(person.name); // 'LISA'
// Inherit
class Shape {
constructor(color) {
this.color = color;
}
draw() {
console.log('Drawing a shape...');
}
}
class Circle extends Shape {
constructor(color, radius) {
super(color);
this.radius = radius;
}
draw() {
console.log(`Drawing a ${this.color} circle with radius ${this.radius}.`);
}
}
const circle = new Circle('red', 10);
circle.draw(); // 'Drawing a red circle with radius 10.'
// Polymorphism
function drawShape(shape) {
shape.draw();
}
drawShape(new Shape('blue')); // 'Drawing a shape...'
drawShape(new Circle('green', 20)); // 'Drawing a green circle with radius 20.'
Conclusion
In this article, I introduced some advanced knowledge points of JavaScript , such as advanced data structures and algorithms, functional programming, asynchronous programming, and object-oriented programming.
📖 Implement concurrent requests through Promise.all
function fetchData(urls) {
const promises = urls.map((url) => fetch(url));
return Promise.all(promises).then((responses) =>
Promise.all(
responses.map((response) => {
if (!response.ok) throw new Error(response.statusText);
return response.json();
})
)
);
}
📖 Use async/await to implement asynchronous calls
async function getData(url) {
const response = await fetch(url);
if (!response.ok) throw new Error(response.statusText);
const data = await response.json();
return data;
}
📖 Using factory pattern in object-oriented programming
class Product {
constructor(name, price) {
this.name = name;
this.price = price;
}
}
class ProductFactory {
createProduct(name, price) {
return new Product(name, price);
}
}
const productFactory = new ProductFactory();
const product = productFactory.createProduct('Apple', 1);
console.log(product.name); // 'Apple'
console.log(product.price); // 1
The above are some simple examples, but in practice, you need more complex and specific cases to solve real-world problems. I hope this article can provide you with some starting points, so that everyone can better understand the advanced usage of JavaScript and become a JavaScript master.
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