Get JavaScript Objects from a JSON File

Introduction

JSON stands for JavaScript Object Notation.JSON is a lightweight format for storing and transporting data.JSON is often used when data is sent from a server to a web page.JSON is "self-describing" and easy to understand. JavaScript objects are an integral part of the React app, so they need to get accessed from JSON files/data to be uses in components.

This blog will demonstrate how to get a JavaScript object from a JSON file or access it using a fetch() HTTP request.

Rendering Values from a JSON File

Create one sample JSON file as given below, and save it as data.json

{
"employees":{
"employee1": {"firstName":"John", "lastName":"Doe"},
"employee2": {"firstName":"Anna", "lastName":"Smith"},
"employee3": {"firstName":"Peter", "lastName":"Jones"}
}
}

Now, if you want to render any of the key-value pairs from the JSON, the .map() function would be useful to iterate the objects; the example is below.

import React, { Component } from "react";
// Import local JSON file
import Data from "./data";

export class Sample extends Component {
  render() {
    return (
      <>
        <div>
          <h3>Using local JSON file</h3>
          {Object.keys(Data.employees).map((item, i) => (
            <li key={i}>
              <span>Key name : {item}</span>
            </li>
          ))}
        </div>
      </>
    );
  }
}

export default Sample;

In the above example, to use the local JSON file needs to be consumed using the import statement.

import Data from "./data";

After that, you can access all the JSON data using Data in your component by using Object.keys() along with the .map() function.

{Object.keys(Data.employees).map((item, i) => ())}

Using a local JSON file in the React app is a common approach when you want to render some static data, maintain server config, etc.

Rendering JSON Objects from an API Call

You have seen the example where a local JSON file is used, but at the same time you may need to access JSON data from the server.

Implement the API call as demonstrated below.

componentDidMount() {
    fetch("https://jsonplaceholder.typicode.com/users")
      .then(res => res.json())
      .then(
        result => {
          this.setState({
            data: result
          });
        },
        error => {
          console.log(error);
        }
      );
}

After implementing the API call, you can access the JSON data for the rendering as below.

render() {
    return (
      <>
        <div>
          <h3>Using API call</h3>
          {this.state.data &&
            this.state.data.length > 0 &&
            this.state.data.map((item, i) => (
              <li key={i}>
                <span>Email : {item.email}</span>
              </li>
            ))}
        </div>
      </>
    );
}

Along with the state this.state.data, the additional function used is .map(), which iterates the array items from the state and renders them into the DOM.

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