Amazing nodejs code

Node.js is an interpreter of the JavaScript language. It can be used to develop various types of applications such as server applications and command line tools. It has the advantages of fast, scalable, and efficient, and has gained more and more attention. Developer favor. This article will introduce some highlight features and excellent code examples of Node.js, hoping to help readers better understand and use Node.js.

1. Asynchronous programming

The most significant feature of Node.js is asynchronous programming. Since Node.js is a single-threaded model, all I/O operations are asynchronous, which makes It performs well with high concurrency and large data volumes. Node.js implements asynchronous processing through callback functions, which improves the efficiency of the entire application in processing I/O.

The following is a simple example:

// 异步读取文件
const fs = require('fs');
fs.readFile('test.txt', function (err, data) {
  if (err) throw err;
  console.log(data);
});
console.log('程序执行完毕');

Running result:

程序执行完毕
<Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>

As you can see, the program first outputs "Program execution completed" and then outputs the file content. This is because file reading is asynchronous, and the callback function cannot be executed until the file reading is completed.

Asynchronous programming can effectively improve the performance and concurrency capabilities of Node.js, but it will also increase the complexity of the code and the difficulty of debugging. In order to avoid excessive nesting of callbacks, Node.js also provides other asynchronous programming methods, such as Promise and Async/Await.

2. Modular development

Node.js supports modular development, which can split the application into multiple modules. Each module is responsible for a function, which facilitates code reuse and maintenance. Node.js modules can be code written by yourself or third-party libraries. They are usually released in the form of npm packages for everyone to install and use.

The following is an example of a custom module:

// greeter.js
function greet(name) {
    console.log(`Hello, ${name}!`);
}
module.exports = {
    greet
}

// main.js
const greeter = require('./greeter');
greeter.greet('John');

Running result:

Hello, John!

Among them, greeter.js is a custom module,# The ##greet function is used to output greetings, and module.exports is used to expose the contents of the module to the outside. Introduce the greeter module through the require function in main.js, and then call the greet function in it.

Modular development can make the code clearer and easier to maintain, and also makes it easier for your code to be used and shared by others.

3. Web development

Node.js can also be used to develop web applications. With the help of frameworks such as Express, you can easily build a web application.

The following is a Hello World example using the Express framework:

const express = require('express');
const app = express();
app.get('/', function (req, res) {
  res.send('Hello World!');
});
app.listen(3000, function () {
  console.log('Example app listening on port 3000!');
});

After installing the Express framework through

npm install express --save, you can use requireFunction to introduce the framework. Then define the route through the app.get function. When the requested URL is /, Hello World! is output. Finally, the server program is started through the app.listen function.

Node.js web development has good scalability and flexibility, and is very similar to the front-end JavaScript language, and the development threshold is low.

4. Testing

The testing framework of Node.js is very mature, and you can use Mocha, Jasmine, Chai and other frameworks for unit testing, integration testing and other types of testing.

The following is a simple test example using the Mocha framework:

const assert = require('assert');
describe('Array', function() {
  describe('#indexOf()', function() {
    it('should return -1 when the value is not present', function() {
      assert.equal([1,2,3].indexOf(4), -1);
    });
  });
});

Use the

describe function and the it function in the test file to define the test case , and then use assert.equal to assert whether the test results are as expected. If the test results do not meet expectations, the Mocha framework will output detailed error information to facilitate developers to debug and troubleshoot problems.

Testing is an important means to ensure application quality and an essential part of the Node.js application development process.

Summary

This article introduces the highlight functions and excellent code examples of Node.js in asynchronous programming, modular development, web development and testing, etc. I hope it can help readers better understand and Use Node.js. As Node.js continues to develop and improve, it will be applied in a wider range of fields, and developers will have more opportunities to accumulate practical experience and excellent code, jointly promoting the prosperity and development of the Node.js ecosystem.

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