Introduction to jsonmask

jsonmask is a powerful tool that allows you to filter JSON objects by a specified mask. It is particularly useful in API development where you need to control the fields returned by an API endpoint, ensuring that clients receive only the data they need. This can reduce payload size, improve performance, and enhance security.

Basic Usage

To get started with jsonmask, you first need to understand its core functionality: filtering JSON objects. Here’s a simple example:

  const jsonmask = require('jsonmask');
  const data = {name: "John", age: 30, city: "New York"};
  const mask = "name,city";
  const result = jsonmask(data, mask);
  console.log(result); // {name: "John", city: "New York"}

Nested Objects

jsonmask supports filtering nested objects as well. Suppose you have more complex data:

  const data = {
    user: {
      name: "John", 
      age: 30
    },
    address: {
      city: "New York",
      country: "USA"
    }
  };
  const mask = "user(name),address(city)";
  const result = jsonmask(data, mask);
  console.log(result); // {user: {name: "John"}, address: {city: "New York"}}

Arrays

Filtering can also be applied within arrays:

  const data = {
    users: [
      {name: "John", age: 30},
      {name: "Jane", age: 25}
    ]
  };
  const mask = "users(name)";
  const result = jsonmask(data, mask);
  console.log(result); // {users: [{name: "John"}, {name: "Jane"}]}

Combining Multiple Masks

You can combine multiple masks to refine your filtering:

  const data = {
    user: {name: "John", age: 30, email: "john@example.com"},
    posts: [
      {title: "Post1", content: "Content1"},
      {title: "Post2", content: "Content2"}
    ]
  };
  const mask = "user(name,email),posts(title)";
  const result = jsonmask(data, mask);
  console.log(result); // {user: {name: "John", email: "john@example.com"}, posts: [{title: "Post1"}, {title: "Post2"}]}

App Example

To better understand the power of jsonmask, let’s consider a simple ExpressJS application that uses it:

  const express = require('express');
  const jsonmask = require('jsonmask');
  const app = express();

  const data = {
    user: {name: "John", age: 30, email: "john@example.com"},
    posts: [
      {title: "Post1", content: "Content1"},
      {title: "Post2", content: "Content2"}
    ]
  };

  app.get('/data', (req, res) => {
    const mask = req.query.fields; 
    const result = jsonmask(data, mask);
    res.json(result);
  });

  app.listen(3000, () => {
    console.log('Server is running on port 3000');
  });

In this example, clients can specify the fields they want to retrieve via the fields query parameter.

Conclusion

jsonmask is an invaluable tool for developers working with APIs. By tailoring the responses to include only the necessary data, you can significantly enhance the performance and security of your applications.

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