nodejs synchronous request

Node.js is a JavaScript runtime environment built on the Chrome V8 engine and is based on an event-driven, non-blocking I/O model, which makes it perform well when processing large data collections and high concurrent requests. But in some cases, we need to make synchronous requests, because we need to wait for the previous request to complete before making the next request, which requires some special skills to make synchronous requests.

There are many ways to make synchronous requests in Node.js. The more common methods include: using callbacks, using Promise, and using async/await. The use of these methods will be introduced here.

1. Using callbacks

The earliest asynchronous processing method in Node.js is the callback function. Subsequent operations can be performed in the callback function, or the callback function can be passed as a value to other functions. A callback function is a JavaScript function that can call another function within the function.

When making a synchronous request, you can use the callback function to ensure that the request is completed before performing other operations. For example:

const request = require('request');

request('https://jsonplaceholder.typicode.com/todos/1', function (error, response, body) {
  if (!error && response.statusCode == 200) {
    console.log(body) // 输出请求得到的结果
  }
})

In the above example, we use the request module to make requests and output the results to the console. Since the callback function is processed asynchronously, we need to perform subsequent operations in the callback function. This ensures that other operations can be performed after the request is completed.

2. Using Promise

Promise is a more advanced asynchronous processing method that provides more flexible and readable code. A Promise represents the eventual completion or failure of an asynchronous operation and returns a value. It simplifies the complexity of asynchronous code and supports chained calls.

When using Promise to make synchronous requests, you can use the request-promise module. This module is the Promise version of the request module, which can easily convert request requests into Promise objects to implement synchronous requests. For example:

const rp = require('request-promise');

rp('https://jsonplaceholder.typicode.com/todos/1')
  .then(function (response) {
    console.log(response);
  })
  .catch(function (err) {
    console.log(err);
  });

In the above example, we use the request-promise module to make requests and use Promise objects to process the request results. This ensures that other operations can be performed after the request is completed.

3. Use async/await

async/await is the latest asynchronous processing method in ES2017. It writes asynchronous code in a more synchronous way, making asynchronous code more readable and maintainable.

When using async/await to make synchronous requests, you need to use the request-promise module. For example:

const rp = require('request-promise');

async function getData() {
  const result = await rp('https://jsonplaceholder.typicode.com/todos/1');
  console.log(result);
}

getData().catch((err) => {
  console.error(err);
});

In the above example, we used async/await to encapsulate the request-promise module. Using the async keyword can turn the getData() function into an asynchronous function, and then we use the await keyword to wait for the request to complete before performing other operations inside the function.

Summary

As a high-performance server-side language, Node.js has put its asynchronous processing capabilities into full play. But in some cases, synchronous requests are required. In this case, we can use callbacks, Promise and async/await to make synchronous requests. In actual development, the most appropriate method can be selected according to the actual situation.

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