How to use Node.js to add, delete, modify and query JSON data

Node.js is a fast, extensible JavaScript runtime whose functionality can be extended through the use of various modules. One of them is JSON (JavaScript Object Notation), a lightweight format for storing and exchanging data. In this article, I will show you how to use Node.js to add, delete, modify and query JSON data.

1. Add JSON data

Node.js provides the fs module for reading and writing files. Saving JSON data to a file can be easily done using the fs module.

First, we need to create a JSON object and save it to a file. In the following code snippet, we create a students.json file and write a JSON object to the file:

const fs = require('fs');

const students = {
  "Tom": {
    "age": 18,
    "gender": "male"
  },
  "Lily": {
    "age": 19,
    "gender": "female"
  }
};

fs.writeFile('students.json', JSON.stringify(students), (err) => {
  if (err) throw err;
  console.log('The JSON data has been saved!');
});

In the above code, the method to write the file is fs.writeFile(), It requires three parameters: file name, data and callback function. The callback function accepts an error object as a parameter and returns null if the write is successful.

2. Reading JSON data

Reading JSON data is also very simple. We just need to read the data from the file using the fs.readFile() method and convert it into a JSON object using the JSON.parse() method.

const fs = require('fs');

fs.readFile('students.json', (err, data) => {
  if (err) throw err;
  const students = JSON.parse(data);
  console.log(students);
});

In the above code, we read the students.json file and convert it into a JSON object using the fs.readFile() method. The callback function accepts an error object and data as parameters. If there is an error, the err parameter will contain the error information, otherwise it will contain the contents of the file.

3. Modify JSON data

To modify JSON data, we only need to use JavaScript’s object attribute access symbol (.) or square bracket access symbol ([]) to change Properties in the object.

const fs = require('fs');

fs.readFile('students.json', (err, data) => {
  if (err) throw err;
  const students = JSON.parse(data);
  
  // 修改Tom的年龄为20
  students.Tom.age = 20;
  
  fs.writeFile('students.json', JSON.stringify(students), (err) => {
    if (err) throw err;
    console.log('The JSON data has been updated!');
  });
});

In the above code, we read the students.json file and convert it into a JSON object. We then change Tom's age to 20 and write the changed data back to the file.

4. Delete JSON data

To delete attributes from a JSON object, we can use the delete keyword.

const fs = require('fs');

fs.readFile('students.json', (err, data) => {
  if (err) throw err;
  const students = JSON.parse(data);
  
  // 删除Lily
  delete students.Lily;
  
  fs.writeFile('students.json', JSON.stringify(students), (err) => {
    if (err) throw err;
    console.log('The JSON data has been updated!');
  });
});

In the above code, we delete the Lily property in the students object and write the changed data back to the file.

Summary

This is how to use Node.js to add, delete, modify and query JSON data. Use the fs module to read and write files, use the JSON.parse() method to convert JSON strings to JSON objects, and use the JSON.stringify() method to convert JSON objects to JSON strings. Using these methods, you can easily process JSON data so that it integrates seamlessly with your application.

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