How to modify the content of json file in nodejs

With the popularity of web applications, JavaScript programming language is no longer limited to browser-side scripting language. Node.js is a back-end runtime environment written in JavaScript. It uses the V8 engine to interpret and execute JavaScript code, providing extremely efficient and convenient development experience. In Node.js, modifying the content of JSON files is one of the common tasks. In this article, we will introduce how to use Node.js to modify the content of a JSON file.

What is JSON?

JSON (JavaScript Object Notation) is a lightweight data exchange format that is extended by the object and array structures in the JavaScript language. In JSON, data is represented in the form of key-value pairs. JSON format data is usually used for data transmission in web applications, but it is also widely used in logging, configuration files and other scenarios.

Development environment and preparations

Before we start modifying the JSON file, we need to have a basic Node.js development environment. If you have not installed Node.js, you can visit the official website https://nodejs.org/ and download the installation package for the corresponding platform. After the installation is complete, open a terminal or console and enter the following command to check the version:

node -v

If the version information of Node.js can be correctly output, the installation is successful.

In preparation, we also need a JSON file as an example. The following is a sample file named config.json:

{
  "server": {
    "port": 8080,
    "hostname": "localhost"
  },
  "database": {
    "host": "localhost",
    "port": 3306,
    "username": "root",
    "password": "password",
    "database": "example_db"
  }
}

The above is a typical JSON file, which contains two top-level keys: server and database. The server key contains two subkeys: port and hostname, and the database key contains five subkeys: host, port, username, password, and database.

Read JSON file content

Before we start modifying the JSON file, we first need to read its content and parse it into a JavaScript object. Node.js provides a built-in fs (File System) module that can be used to read and write files. The following is a code example that reads the contents of the config.json file:

const fs = require("fs");

const configPath = "./config.json";

fs.readFile(configPath, "utf8", (err, data) => {
  if (err) {
    console.error(err);
    return;
  }

  const config = JSON.parse(data);
  console.log(`Server port: ${config.server.port}`);
  console.log(`Database host: ${config.database.host}`);
});

In the code, the fs module is first introduced and the configPath variable is defined to store the relative path of the config.json file. The contents of the file are then read using the fs.readFile() method and the contents are returned as a UTF-8 encoded string. After the reading is completed, we use the JSON.parse() method to parse the string into a JavaScript object and output the values ​​​​of two of the properties.

Modify the content of the JSON file

There are two ways to modify the content of the JSON file: one is to modify the JavaScript object directly in the memory and then write it to the file; the other is to modify the JSON A key-value pair in the file and writes it to the file. These two methods are introduced below.

Method 1: Modify the JavaScript object in memory

In Node.js, the content of the JSON file after parsing is a JavaScript object. We only need to modify the attribute value of the object in memory. , and then write it into the file to complete the modification of the JSON file. The following is a code example that changes the server port number in config.json to 8888:

const fs = require("fs");

const configPath = "./config.json";

fs.readFile(configPath, "utf8", (err, data) => {
  if (err) {
    console.error(err);
    return;
  }

  const config = JSON.parse(data);
  config.server.port = 8888;

  const updatedConfig = JSON.stringify(config, null, 2);

  fs.writeFile(configPath, updatedConfig, (err) => {
    if (err) {
      console.error(err);
      return;
    }

    console.log("Config file updated successfully.");
  });
});

In the code, we first read the contents of the config.json file and parse it into a JavaScript object stored in the config variable middle. Then change the port number from 8080 to 8888 by modifying the server.port property of the config object. Then use the JSON.stringify() method to convert the modified object into a JSON string, and set the indentation to 2 spaces for easier reading. Finally, use the fs.writeFile() method to write the updated JSON string into the config.json file.

Method 2: Modify the key-value pairs in the JSON file

If we only need to modify a certain key-value pair in the JSON file, rather than the entire file content, we can read the JSON directly file, modifies the specified key-value pair, and writes them back to the file. The following is a code example to change the database password in config.json to new_password:

const fs = require("fs");
const configPath = "./config.json";

fs.readFile(configPath, "utf8", (err, data) => {
  if (err) {
    console.error(err);
    return;
  }

  const config = JSON.parse(data);
  config.database.password = "new_password";

  const updatedConfig = JSON.stringify(config, null, 2);

  const options = { flag: "w" };
  fs.writeFile(configPath, updatedConfig, options, (err) => {
    if (err) {
      console.error(err);
      return;
    }

    console.log("Config file updated successfully.");
  });
});

In the code, we first read the contents of the config.json file and parse it into a JavaScript object and store it in the config variable . Then change the password from password to new_password by modifying the database.password attribute of the config object. Then use the JSON.stringify() method to convert the modified object into a JSON string, and set the indent to 2 spaces. Finally, use the fs.writeFile() method to write the updated JSON string back to the config.json file, and use the w flag to indicate overwriting the original file.

Summary

Using Node.js to modify the content of a JSON file is generally divided into two methods: modifying JavaScript objects in memory or directly modifying key-value pairs in the JSON file. The former is suitable for modifying the entire JSON file, and the latter is suitable for modifying only a certain key-value pair. During the operation, you need to pay attention to details such as the format of the JSON file and the callback functions for reading and writing files. After mastering these skills, we can easily use Node.js to modify the content of JSON files.

The above is the detailed content of How to modify the content of json file in nodejs. For more information, please follow other related articles on the PHP Chinese website!