For AI agents: the complete documentation index is available at /llms.txt, the full documentation bundle is available at /llms-full.txt, and this page is available as Markdown at /reference/array/isSubsetWith.md.
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    isSubsetWith es-toolkit

    Checks if one array is a subset of another array based on a custom comparison function.

    const result = isSubsetWith(superset, subset, areItemsEqual);

    Usage

    isSubsetWith(superset, subset, areItemsEqual)

    Use isSubsetWith when you want to verify a subset relationship using a user-defined comparison function. This is useful when comparing objects or when special comparison logic is needed.

    import { isSubsetWith } from 'es-toolkit/array';

// Check subset by object's id
const users = [
  { id: 1, name: 'john' },
  { id: 2, name: 'jane' },
  { id: 3, name: 'bob' },
];
const targetUsers = [
  { id: 2, name: 'jane' },
  { id: 1, name: 'john' },
];
isSubsetWith(users, targetUsers, (a, b) => a.id === b.id);
// Returns: true

// When it's not a subset
const allUsers = [
  { id: 1, name: 'john' },
  { id: 2, name: 'jane' },
];
const someUsers = [{ id: 3, name: 'bob' }];
isSubsetWith(allUsers, someUsers, (a, b) => a.id === b.id);
// Returns: false

    Complex comparison logic can also be used.

    import { isSubsetWith } from 'es-toolkit/array';

// Case-insensitive string comparison
const validNames = ['Alice', 'Bob', 'Charlie'];
const userNames = ['alice', 'BOB'];
isSubsetWith(validNames, userNames, (a, b) => a.toLowerCase() === b.toLowerCase());
// Returns: true

// Number comparison within a range
const validRanges = [1, 2, 3, 4, 5];
const testNumbers = [1.1, 2.8];
isSubsetWith(validRanges, testNumbers, (a, b) => Math.abs(a - b) < 0.5);
// Returns: true (1.1 is close enough to 1, 2.8 is close enough to 3)

    Parameters

    supersetreadonly T[]required

    The superset array that may contain all elements of the subset.

    subsetreadonly T[]required

    The subset array to check if it's contained in the superset.

    areItemsEqual(x: T, y: T) => booleanrequired

    A function to determine if two elements are equal. Should return true if equal, false otherwise.

    Returns

    Based on the custom comparison function, returns true if all elements of the subset are contained in the superset, otherwise returns false.

    boolean
    Source: es-toolkit

    Re-exported verbatim from es-toolkit. Implementation, edge cases, and performance behavior are owned upstream. This page mirrors the documentation at the pinned version; the linked source is authoritative.