@ckeditor/ckeditor5-utils/src/comparearrays.js

Miscellaneous utilities used by CKEditor 5.

/**
 * @license Copyright (c) 2003-2025, CKSource Holding sp. z o.o. All rights reserved.
 * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-licensing-options
 */
/**
 * @module utils/comparearrays
 */
/**
 * Compares how given arrays relate to each other. One array can be: same as another array, prefix of another array
 * or completely different. If arrays are different, first index at which they differ is returned. Otherwise,
 * a flag specifying the relation is returned. Flags are negative numbers, so whenever a number >= 0 is returned
 * it means that arrays differ.
 *
 * ```ts
 * compareArrays( [ 0, 2 ], [ 0, 2 ] );		// 'same'
 * compareArrays( [ 0, 2 ], [ 0, 2, 1 ] );		// 'prefix'
 * compareArrays( [ 0, 2 ], [ 0 ] );			// 'extension'
 * compareArrays( [ 0, 2 ], [ 1, 2 ] );		// 0
 * compareArrays( [ 0, 2 ], [ 0, 1 ] );		// 1
 * ```
 *
 * @param a Array that is compared.
 * @param b Array to compare with.
 * @returns How array `a` is related to `b`.
 */
export default function compareArrays(a, b) {
    const minLen = Math.min(a.length, b.length);
    for (let i = 0; i < minLen; i++) {
        if (a[i] != b[i]) {
            // The arrays are different.
            return i;
        }
    }
    // Both arrays were same at all points.
    if (a.length == b.length) {
        // If their length is also same, they are the same.
        return 'same';
    }
    else if (a.length < b.length) {
        // Compared array is shorter so it is a prefix of the other array.
        return 'prefix';
    }
    else {
        // Compared array is longer so it is an extension of the other array.
        return 'extension';
    }
}