How to Load Data from a File in Next.js?

Last Updated : 01 May, 2024

Loading Data from files consists of using client-side techniques to read and process files in a Next.js application.

In this article, we will explore a practical demonstration of Load Data from a File in Next.js. We will load a validated CSV input file and display its contents in tabular format.

Approach

The FileReader API is used to read the contents of the uploaded file.
The uploaded file is validated to ensure it is a CSV file before processing.
The CSV data is parsed and displayed in a tabular format once the file is successfully processed.
The useState hook is used to manage state variables for storing CSV data, error messages, and loading status.
The handleFileUpload() function is triggered when a file is selected by the user for upload.
Error messages are displayed if the user uploads a file that is not in CSV format or if no file is selected.
The CSV data is split into rows and cells, then rendered in a tabular format using HTML <table> and <td> elements.

Steps to Create the Next.js Application

Step 1: Set up React Project using the Command:

npx create-next-app url-domain

Step 2: Navigate to the Project folder using:

cd url-domain

Project Structure:

The updated dependencies in package.json file will look like:

  "dependencies": {
    "react": "^18",
    "react-dom": "^18",
    "next": "14.2.1"
  }

Example: The below example demonstrates the Loading Data from a File in Next.JS.

JavaScript

//page.js
"use client";
import React, { useState } from 'react';
const Page = () => {
  const [csvData, setCsvData] = useState([]);
  const [errorMessage, setErrorMessage] = useState('');
  const [isLoading, setIsLoading] = useState(false);
  const handleFileUpload = (event) => {
    const file = event.target.files[0];
    if (!file) {
      setErrorMessage('Please select a file.');
      return;
    }
    if (!file.name.endsWith('.csv')) {
      setErrorMessage('Please upload a CSV file.');
      return;
    }
    setIsLoading(true);
    const reader = new FileReader();
    reader.onload = (e) => {
      const text = e.target.result;
      const rows = text.split('\n').map((row) => row.split(','));
      setCsvData(rows);
      setErrorMessage('');
      setIsLoading(false);
    };
    reader.readAsText(file);
  };
  return (
    <div style={{ padding:'20px', maxWidth:'800px', margin:'0 auto' }}>
      <h1 style={{marginBottom: '20px' }}>
          Loading Data from File
      </h1>
      <input type="file" onChange={handleFileUpload} 
            accept=".csv" style={{ marginBottom: '10px' }} 
      />
      { errorMessage && <div style={{color:'red', marginBottom:'10px' }}>
        { errorMessage }</div> 
      }
      { isLoading ? 
        (
          <div style={{ textAlign:'center', marginTop:'20px' }}>
            Loading...
          </div>
        ) : 
        (
          csvData.length > 0 && ( 
          <table style={{ borderCollapse:'collapse', 
                          width:'100%', marginTop:'20px' }}>
            <tbody>
              { csvData.map((row, index) => (
                <tr key={index}>
                  { row.map((cell, cellIndex) => (
                    <td key={cellIndex} 
                        style={{ border:'1px solid #ccc', padding:'8px' }}>
                        {cell}
                    </td>
                  ))}
                </tr>
                ))
              }
            </tbody>
          </table>
          )
        )
      }
    </div>
  );
};
export default Page;