Find Missing Elements

findMissingElements

Performs a deep comparison between two arrays and returns elements missing from one array relative to the other. It allows you to specify the direction of comparison to extract missing values from either array.

Function Signature

function findMissingElements<T, U>(
  array1: T[],
  array2: U[],
  missingFrom: 'from-first' | 'from-second'
): (T | U)[];

Parameters

Parameter	Type	Description
array1	T[]	First array to compare
array2	U[]	Second array to compare
missingFrom	'from-first' | 'from-second'	Direction of comparison: - 'from-first': Finds elements in array1 missing from array2 - 'from-second': Finds elements in array2 missing from array1

Returns

• (T | U)[]: An array containing elements present in the source array but missing in the target array (based on deep equality comparison).

Example Usage

import { findMissingElements } from 'nhb-toolbox';

const array1 = [{ id: 1 }, { id: 2 }, { id: 3 }];
const array2 = [{ id: 1 }, { id: 3 }, { id: 4 }];

// Find elements in array1 missing from array2
console.log(findMissingElements(array1, array2, 'from-first'));
// Output: [{ id: 2 }]

// Find elements in array2 missing from array1
console.log(findMissingElements(array1, array2, 'from-second'));
// Output: [{ id: 4 }]

Notes

• Performs deep equality comparison (handles objects and nested structures)
• Preserves original element references
• Returns empty array if no differences found
• Works with arrays of different types (T and U)

Comparison Logic

1. 'from-first' mode:

   array1.filter(item => !array2.some(item2 => isDeepEqual(item, item2)))

2. 'from-second' mode:

   array2.filter(item => !array1.some(item1 => isDeepEqual(item, item1)))

Use Cases

• Detecting changes between datasets
• Finding deleted/added items in collections
• Data synchronization
• Array difference operations
• State comparison in applications

Conclusion

The findMissingElements function provides:

1. Flexible comparison direction
2. Deep equality checking
3. Type-safe operations
4. Clear results for array differences

Ideal for applications requiring:

• Data synchronization
• Change detection
• State management
• Collection comparisons