How to Flatten and Unflatten Deeply Nested JSON Objects in JavaScript

The Challenge of Deeply Nested Payloads

Modern REST and GraphQL APIs commonly return objects nested 4 to 8 levels deep. While convenient for object-oriented programming, deep nesting creates architectural obstacles when: - Exporting customer records to flat CSV spreadsheets - Indexing document properties in search engines like Elasticsearch - Ingesting semi-structured records into relational SQL databases

Efficient Recursive Flattening in JavaScript

Here is a dependency-free, zero-copy flattening function that traverses objects and arrays recursively:

function flattenObject(obj, prefix = '', result = {}) {
  for (const [key, value] of Object.entries(obj)) {
    const newKey = prefix ? `${prefix}.${key}` : key;
    if (value !== null && typeof value === 'object' && !Array.isArray(value)) {
      flattenObject(value, newKey, result);
    } else {
      result[newKey] = value;
    }
  }
  return result;

// Example usage: const nested = { user: { profile: { name: "Alice", active: true } } }; console.log(flattenObject(nested)); // Outputs: { "user.profile.name": "Alice", "user.profile.active": true } ```

Unflattening Dot-Notation Back to Nested Trees

To restore a flattened object back to its original hierarchical structure:

function unflattenObject(data) {
  const result = {};
  for (const [key, value] of Object.entries(data)) {
    const keys = key.split('.');
    let current = result;
    keys.forEach((part, index) => {
      if (index === keys.length - 1) {
        current[part] = value;
      } else {
        current[part] = current[part] || {};
        current = current[part];
      }
    });
  }
  return result;
}

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