Menguasai Konsep Teras JavaScript untuk Pembangun Node.js
JavaScript telah mendahului dalam pengekodan dengan menjadi bahasa pilihan untuk pembangunan bahagian hadapan dan belakang, dengan NodeJs di hadapan. Sebelum buzz di sekitar JavaScript bahagian pelayan menjadi keren, semua orang mengiktiraf JS sebagai hebat pergerakan itu. Walaupun platform yang lebih baharu seperti Deno dan Bun telah mula menyediakan persaingan, NodeJs kekal sebagai tulang belakang aplikasi web dan perisian sistem, dengan berjuta-juta baris kod yang ditulis dan dilaksanakan menggunakan JS. Dibina pada seni bina berbenang tunggal, tak segerak dan alatannya yang unik seperti Express, NodeJs merupakan satu kebaikan dan keburukan bagi pembangun. Untuk menulis aplikasi yang cekap, berskala dan boleh diselenggara, adalah penting untuk memahami konsep JavaScript utama.
Konsep teras ini menggerakkan anda melangkaui cabaran biasa seperti penjalinan, skop penutupan dan kod tak segerak, mengeluarkan JavaScript dalam NodeJs untuk kuasa maksimum. Panduan ini merangkumi 18 teknik JavaScript yang paling penting untuk membantu anda menulis kod yang kompleks dan berprestasi sambil mengelakkan perangkap biasa dan menavigasi gelung acara dengan berkesan. Sama ada anda sedang mengusahakan API, operasi I/O atau pengoptimuman memori, menguasai konsep ini akan meningkatkan pembangunan NodeJs anda ke peringkat seterusnya.
1. Penutupan JavaScript
Contoh:
function outerFunction() { const outerVariable = "I am from outer function!"; return function innerFunction() { console.log(outerVariable); }; } const innerFunc = outerFunction(); innerFunc(); // Output: "I am from outer function!"
Contoh ini menunjukkan penutupan di mana fungsi dalam mengekalkan akses kepada pembolehubah fungsi luar walaupun selepas ia selesai melaksanakan.
2. Prototaip JavaScript
Contoh:
function Person(name) { this.name = name; } Person.prototype.greet = function() { console.log(`Hello, my name is ${this.name}`); }; const john = new Person("John"); john.greet(); // Output: "Hello, my name is John"
Di sini, salam ditakrifkan pada prototaip Orang, membenarkan semua kejadian Orang berkongsi kaedah ini, yang menjimatkan memori.
3. Harta Peribadi dengan Hashtag
Contoh:
class User { #name; // Private property constructor(name) { this.#name = name; } getName() { return this.#name; } } const user = new User("Alice"); console.log(user.getName()); // Output: "Alice" // console.log(user.#name); // Error: Private field '#name' must be declared in an enclosing class
Contoh ini menunjukkan cara simbol # digunakan untuk mengisytiharkan harta yang benar-benar peribadi yang tidak boleh diakses dari luar kelas.
4. Hartanah Persendirian dengan Penutupan
Contoh:
function createCounter() { let count = 0; // Private variable return { increment: function() { count++; }, getCount: function() { return count; } }; } const counter = createCounter(); counter.increment(); console.log(counter.getCount()); // Output: 1
Dalam contoh ini, kira dirangkumkan dalam penutupan, memberikan keadaan peribadi untuk kaunter.
5. Modul JavaScript
Contoh:
// module.js export const greeting = "Hello, World!"; export function greet() { console.log(greeting); } // main.js import { greet } from './module.js'; greet(); // Output: "Hello, World!"
This example illustrates how to use ES6 modules to export and import variables and functions between files.
6. Error Handling
Example:
async function fetchData() { try { const response = await fetch('https://api.example.com/data'); if (!response.ok) throw new Error('Network response was not ok'); const data = await response.json(); console.log(data); } catch (error) { console.error('Fetch error:', error); } } fetchData(); // Handles fetch errors gracefully.
Here, error handling is implemented using try/catch with asynchronous code to manage potential errors when fetching data.
7. Currying
Example:
function multiply(a) { return function(b) { return a * b; }; } const double = multiply(2); console.log(double(5)); // Output: 10
In this example, the multiply function is curried, allowing for partial application by creating a double function.
8. Apply, Call, and Bind Methods
Example:
const obj = { value: 42 }; function showValue() { console.log(this.value); } showValue.call(obj); // Output: 42 showValue.apply(obj); // Output: 42 const boundShowValue = showValue.bind(obj); boundShowValue(); // Output: 42
This example demonstrates how call, apply, and bind control the context of this when invoking functions.
9. Memoization
Example:
function memoize(fn) { const cache = {}; return function(...args) { const key = JSON.stringify(args); if (cache[key]) return cache[key]; const result = fn(...args); cache[key] = result; return result; }; } const fibonacci = memoize(n => (n <= 1 ? n : fibonacci(n - 1) + fibonacci(n - 2))); console.log(fibonacci(10)); // Output: 55 (calculated efficiently)
This example shows how memoization can optimize the Fibonacci function by caching results of previous calls.
10. Immediately Invoked Function Expressions (IIFE)
Example:
(function() { const privateVariable = "I'm private!"; console.log(privateVariable); })(); // Output: "I'm private!"
An IIFE is used here to create a scope that keeps privateVariable from polluting the global namespace.
11. Working with Function Arguments
Example:
function sum(...numbers) { return numbers.reduce((total, num) => total + num, 0); } console.log(sum(1, 2, 3, 4)); // Output: 10
This example uses the rest operator to collect multiple arguments into an array, allowing flexible function signatures.
12. Asynchronous Programming and the Event Loop
Example:
console.log("Start"); setTimeout(() => { console.log("Timeout executed"); }, 1000); console.log("End"); // Output: "Start", "End", "Timeout executed" (after 1 second)
This example illustrates how the event loop manages asynchronous code, allowing other operations to run while waiting for the timeout.
13. Promises and async/await
Example:
function fetchData() { return new Promise((resolve) => { setTimeout(() => resolve("Data received"), 1000); }); } async function getData() { const data = await fetchData(); console.log(data); // Output: "Data received" } getData();
This example demonstrates the use of async/await to work with promises in a more readable way.
14. Event Emitters
Example:
const EventEmitter = require('events'); const myEmitter = new EventEmitter(); myEmitter.on('event', () => { console.log('An event occurred!'); }); myEmitter.emit('event'); // Output: "An event occurred!"
Here, an event emitter is created, and an event is triggered, demonstrating the basic event-driven architecture of Node.js.
15. Streams and Buffers
Example:
const fs = require('fs'); const readableStream = fs.createReadStream('file.txt'); readableStream.on('data', (chunk) => { console.log(`Received ${chunk.length} bytes of data.`); }); readableStream.on('end', () => { console.log('No more data.'); });
This example shows how to read data from a file in chunks using streams, which is efficient for large files.
16. Higher-Order Functions
Example:
function applyOperation(a, b, operation) { return operation(a, b); } const add = (x, y) => x + y; console.log(applyOperation(5, 10, add)); // Output: 15
In this example, applyOperation is a higher-order function that takes another function as an argument to perform operations on the inputs.
17. Garbage Collection and Memory Management
Example:
function createLargeArray() { const largeArray = new Array(1000000).fill('Data'); // Do something with the array } createLargeArray(); // The largeArray will be eligible for garbage collection after this function execution
This example illustrates how objects can be garbage collected when they are no longer accessible, thus freeing up memory.
18. Timers
Example:
console.log('Start'); setTimeout(() => { console.log('Executed after 2 seconds'); }, 2000); setInterval(() => { console.log('Executed every second'); }, 1000);
In this example, setTimeout schedules a one-time execution after 2 seconds, while setInterval repeatedly executes the function every second.
19. Template Literals
Example:
const name = "Alice"; const greeting = `Hello, ${name}! Welcome to JavaScript.`; console.log(greeting); // Output: Hello, Alice! Welcome to JavaScript.
In this example, template literals are used to create a greeting string that incorporates a variable directly within the string.
20. Destructuring Assignment
Example:
const user = { id: 1, name: "Bob", age: 30 }; const { name, age } = user; console.log(name); // Output: Bob console.log(age); // Output: 30
This example demonstrates how to extract properties from an object into individual variables, making the code cleaner and more concise.
Conclusion
Using these core JavaScript concepts, you will write scalable, efficient, and maintainable NodeJs applications. NodeJs is built on JavaScript's event-driven and asynchronous nature, so you should have a good grasp of these concepts at this point. Beyond these 20 points, the more you learn about Node.js feature changes and patterns, the better your NodeJs development skills will become.
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