How to make synchronous HTTP requests in JavaScript?

In the current digital landscape, the act of making an HTTP request is an essential part of transmitting and receiving data between a client and a server. Asynchronous requests have become popular because they provide a non-blocking experience, which ultimately enhances the overall user experience. However, in some cases, synchronous HTTP requests may prove necessary or preferable. In the following narrative, we will delve into algorithms for creating synchronous HTTP requests using JavaScript. We will also explore two different approaches and their corresponding code explanations and practical applications.

algorithm

To make a synchronous HTTP request in JavaScript, a basic algorithm must be executed that includes subsequent stages -

• First, generate an example of an HTTP request object.

• Second, adjust the request by specifying the methodology, Uniform Resource Locator (URL), and enabling request synchronization mode.

• Third, send the request.

• Fourth, wait for a reply.

• Finally, handle the response accordingly.

method

Using XMLHttpRequest

XMLHttpRequest is a pre-existing object in JavaScript that has been used for quite some time. Although it has been superseded by modern alternatives, it still performs synchronous HTTP requests very well. Here are instructions on how to implement XMLHttpRequest -

function synchronousRequest(url) {
   const xhr = new XMLHttpRequest();
   xhr.open('GET', url, false);
   xhr.send(null);
   if (xhr.status === 200) {
      return xhr.responseText;
   } else {
      throw new Error('Request failed: ' + xhr.statusText);
   }
}

In this example, we first create a new XMLHttpRequest instance. Next, we call the open() method to configure the request. The first parameter is the HTTP method (GET), the second parameter is the URL, and the third parameter is a Boolean value indicating whether the request should be asynchronous (false for synchronous requests). Finally, we send the request using the send() method and wait for the response. If the status is 200 (OK), we return the response text; otherwise, we throw an error.

Example

Use the synchronousRequest function defined earlier -

try {
   const url = 'https://api.example.com/data';
   const responseData = synchronousRequest(url);
   console.log('Response data:', responseData);
} catch (error) {
   console.error('Error:', error.message);
}

In this example, we call the synchronousRequest function using the prototype URL. If the request is successful, we will log the response information to the console. However, if it fails, we log an error message to the console.

Use Get API

The Fetch API is a modern replacement for XMLHttpRequest, designed to be more flexible and easier to use. Unfortunately, the native fetch() function does not support synchronous requests. However, you can use async/await to create sync-like behavior -

async function synchronousFetch(url) {
   const response = await fetch(url);
   if (response.ok) {
      const data = await response.text();
      return data;
   } else {
      throw new Error('Request failed: ' + response.statusText);
   }
}

In this example, we use the fetch() function to provide Promise. We use the await keyword to pause execution until the Promise ends before continuing with subsequent lines of code. If the response is satisfactory, we retrieve the response text; otherwise, we trigger an error.

Example

Use the synchronousFetch function defined earlier -

import React, { useEffect, useState } from "react";
import "./styles.css";
export default function App() {
   const [responseData, setResponseData] = useState(null);
   useEffect(() => {
      (async () => {
         try {
            const url = "https://jsonplaceholder.typicode.com/todos/1";
            const response = await fetch(url);
            if (!response.ok) {
               throw new Error(`HTTP error! Status: ${response.status}`);
            }
            const data = await response.json();
            setResponseData(data);
         } catch (error) {
            console.error("Error:", error.message);
         }
      })();
   }, []);
   return (
      <div className="App">
         <h1>API Data</h1>
         {responseData ? (
            <pre class="brush:php;toolbar:false">{JSON.stringify(responseData, null, 2)}

) : (

Loading...

)}

); }

Copy after login

Output

API Data
{
   "userId": 1,
   "id": 1,
   "title": "delectus aut autem",
   "completed": false
}

In this example, we call the synchronousFetch function in the asynchronous function to correctly handle the wait keyword. As in the previous example, we log the response data to the console if the request is successful, otherwise an error message is logged.

in conclusion

While asynchronous requests are generally favored for their non-blocking nature, synchronous HTTP requests in JavaScript still have their use cases. We discussed algorithms for making synchronous HTTP requests and explored two different approaches, including the older XMLHttpRequest method and the more modern Fetch API with async/await. Keep in mind that synchronous requests should be used with caution, as they can block the execution of JavaScript code and negatively impact the user experience.

The above is the detailed content of How to make synchronous HTTP requests in JavaScript?. For more information, please follow other related articles on the PHP Chinese website!