JSON to CSV Conversion: Complete Developer Guide

Basic JSON to CSV Conversion in JavaScript

// Simple flat JSON array to CSV
function jsonToCsv(jsonArray) {
  if (!jsonArray || jsonArray.length === 0) return '';
  
  // Get headers from first object
  const headers = Object.keys(jsonArray[0]);
  
  // Create CSV header row
  const headerRow = headers.map(h => `"${h}"`).join(',');
  
  // Create data rows
  const dataRows = jsonArray.map(obj => 
    headers.map(header => {
      const value = obj[header];
      // Handle null, undefined, and special characters
      if (value === null || value === undefined) return '';
      // Escape quotes and wrap in quotes
      const stringValue = String(value).replace(/"/g, '""');
      return `"${stringValue}"`;
    }).join(',')
  );
  
  return [headerRow, ...dataRows].join('\n');
}

// Example usage
const users = [
  { id: 1, name: "John Doe", email: "john@example.com", age: 30 },
  { id: 2, name: "Jane Smith", email: "jane@example.com", age: 25 }
];

const csv = jsonToCsv(users);
console.log(csv);
// Output:
// "id","name","email","age"
// "1","John Doe","john@example.com","30"
// "2","Jane Smith","jane@example.com","25"

Handling Nested JSON Objects

// Flatten nested objects using dot notation
function flattenObject(obj, prefix = '', result = {}) {
  for (const key in obj) {
    if (obj.hasOwnProperty(key)) {
      const newKey = prefix ? `${prefix}.${key}` : key;
      
      if (typeof obj[key] === 'object' && obj[key] !== null && !Array.isArray(obj[key])) {
        // Recursively flatten nested objects
        flattenObject(obj[key], newKey, result);
      } else {
        // Handle arrays by converting to string
        if (Array.isArray(obj[key])) {
          result[newKey] = obj[key].join('; ');
        } else {
          result[newKey] = obj[key];
        }
      }
    }
  }
  return result;
}

// Convert nested JSON to flat CSV
function nestedJsonToCsv(jsonArray) {
  const flattened = jsonArray.map(obj => flattenObject(obj));
  return jsonToCsv(flattened);
}

// Example with nested data
const nestedData = [
  {
    id: 1,
    name: "John",
    address: { city: "New York", country: "USA" },
    tags: ["developer", "javascript"]
  }
];

const csv = nestedJsonToCsv(nestedData);
// Output includes: "id","name","address.city","address.country","tags"