nodejs asynchronous network request

Node.js is a JavaScript runtime environment built on the Chrome V8 engine. It can use JavaScript to write programs on the server side, supports asynchronous I/O operations, and is suitable for building high-concurrency, low-latency network applications. When developing network applications using Node.js, using asynchronous network requests is a very important technical point.

This article will introduce the relevant knowledge and implementation methods of asynchronous network requests in Node.js.

1. What is asynchronous network request

Before introducing asynchronous network request, let’s first understand the concepts of synchronization and asynchronous.

Synchronous operation means that when performing an operation, you must wait for the previous operation to be completed before proceeding to the next operation. As shown in the following code:

var fs = require('fs');
var data = fs.readFileSync('file.txt');
console.log(data);

The above code is a way to read the file synchronously. The program will print out the data after reading the file.

Asynchronous operation means that when performing an operation, you can proceed to the next operation without waiting for the previous operation to be completed. As shown in the following code:

var fs = require('fs');
fs.readFile('file.txt', function(err, data) {
    console.log(data);
});

The above code is a way to read the file asynchronously. The program will execute the next statement immediately after starting to read the file without waiting for the file reading to complete. After the reading is completed, the callback function will be executed, the read data will be passed to the callback function as a parameter, and the data will be printed out.

Asynchronous operations are very important when processing network requests, because network requests involve factors such as network delay and bandwidth limitations, and the response times of different requests are different. Using asynchronous operations can make full use of CPU resources and improve the concurrent processing capabilities of the program.

2. Asynchronous network requests in Node.js

In Node.js, there are many ways to implement asynchronous network requests. Two common methods are introduced below.

1. http module implements asynchronous network requests

The http module is a module in Node.js specially used to handle HTTP requests. The http module provides the request() method to send HTTP requests and the callback function to process the server response data.

The following is a sample code for the http module to send a GET request:

var http = require('http');

var options = {
    host: 'www.baidu.com',
    port: 80,
    path: '/'
};

http.request(options, function(response) {
    var str = '';
    response.on('data', function(chunk) {
        str += chunk;
    });
    response.on('end', function() {
        console.log(str);
    });
}).end();

In the above code, options defines the relevant parameters for sending a GET request, including the target host, port and path of the request. The request() method returns a writable stream object that can be used to send HTTP requests. When the response data arrives, the response object triggers the data event. You can register the callback function of the data event through the on() method to read each data block into a buffer. At the end of the data transfer, the response object triggers the end event. You can register the callback function of the end event through the on() method. The read buffer data can be processed in the callback function.

2. The request module implements asynchronous network requests

The request module is a third-party module in Node.js, used to send HTTP requests. It is simpler and easier to use than the http module, has stronger scalability, and supports advanced functions such as cookies, redirection, and HTTP proxy.

To use the request module, you first need to install it:

npm install request --save

After the installation is complete, you can use the request module in Node.js. The following is a sample code that uses the request module to send a GET request:

var request = require('request');

request('http://www.baidu.com', function(error, response, body) {
    if (!error && response.statusCode == 200) {
        console.log(body);
    }
});

In the above code, the request() method sends an HTTP request and processes the data returned by the server in the callback function. The request() method accepts two parameters, the first parameter is the requested URL, and the second parameter is the callback function. The parameters of the callback function are error, response and response body. If the request has no errors and the return status code is 200, the response body is printed on the console.

3. Advantages of asynchronous network requests

Using asynchronous network requests has the following advantages:

1. Improving the concurrent processing capabilities of the program

Asynchronous network requests can make full use of CPU resources and improve the concurrent processing capabilities of the program.

2. Reduce request waiting time

Using asynchronous network requests can avoid a request waiting for the response of other requests, thereby reducing waiting time.

3. Reasonable utilization of bandwidth resources

Using asynchronous network requests can initiate other requests while waiting for a response to a request, thereby rationally utilizing bandwidth resources.

4. Precautions for asynchronous network requests

Please pay attention to the following points when using asynchronous network requests:

1. Handling errors

Network requests may have errors, such as network disconnection, server response timeout, etc. Therefore, be sure to handle possible errors in the request in the callback function.

2. Execution order of callback functions

Since asynchronous network requests are non-blocking and event-driven, the execution order of callback functions is uncertain. If multiple asynchronous network requests are issued at the same time, the order of responses cannot be guaranteed.

3. Control the number of concurrent requests

Too many concurrent requests will occupy too much CPU resources, causing the server to respond slowly or cause errors. Therefore, when sending a large number of asynchronous network requests, the number of concurrent requests must be controlled to avoid affecting the normal operation of the server.

5. Summary

Asynchronous network request is a very important technical point in Node.js. This article introduces the relevant knowledge and implementation methods of asynchronous network requests in Node.js. Using asynchronous network requests can improve the program's concurrent processing capabilities, reduce request waiting time, and rationally utilize bandwidth resources. When using asynchronous network requests, pay attention to issues such as handling errors, controlling the number of concurrent requests, and the execution order of callback functions.

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