Skip to main content

Extract Updated Fields

Extracts only the fields that have changed between two objects, including deep/nested changes.

Import​

import { extractUpdatedFields } from 'nhb-toolbox';

Usage​

Basic Usage​

const original = { name: 'John', age: 30 };
const updated = { name: 'John', age: 31 };
const changes = extractUpdatedFields(original, updated); 
// Returns { age: 31 }

Nested Objects​

const v1 = { user: { id: 1, profile: { name: 'Alice' } } };
const v2 = { user: { id: 1, profile: { name: 'Alice', active: true } } };
extractUpdatedFields(v1, v2);
// Returns { user: { profile: { active: true } } }

API Reference​

Type Parameters​

NameDescription
TType of the base object

Parameters​

NameTypeDescription
baseObjectTOriginal reference object
updatedObjectFlattenPartial<T>Object containing potential updates

Returns​

FlattenPartial<T>: New object containing only changed fields (shallow copy)

Behavior​

  1. Value Comparison: Uses deep equality check to detect changes
  2. Nested Objects: Recursively compares nested object structures
  3. Empty Results: Returns empty object if no changes found
  4. Reference Safety: Never modifies input objects

Examples​

Detecting Configuration Changes​

const oldConfig = { theme: 'dark', timeout: 30 };
const newConfig = { theme: 'light', timeout: 30 };
extractUpdatedFields(oldConfig, newConfig);
// { theme: 'light' }

Partial Updates​

const dbRecord = { id: 1, content: 'Hello', meta: { views: 0 } };
const update = { content: 'Updated', meta: { views: 1 } };
extractUpdatedFields(dbRecord, update);
// { content: 'Updated', meta: { views: 1 } }

Limitations​

  1. Circular References: Will fail on circular structures
  2. Special Types: May not handle special objects (Date, RegExp, etc.) as expected
  3. Performance: Deep comparison is slower for large objects
  4. Arrays: Treats array replacements as single changes (does not diff array items)

Type Definitions​

type GenericObject = Record<string, any>;
type FlattenPartial<T> = Partial<{ [K in keyof T]: T[K] }>;

Suggested Use Cases​

  • API patch requests
  • State change detection
  • Configuration management
  • Audit logging
  • Database updates