office-ui-fabric-react/lib/components/Dropdown/utilities/DropdownSizePosCache.js

Reusable React components for building experiences for Office 365.

import { DropdownMenuItemType } from '../Dropdown.types';
/**
 * A utility class to cache size and position in cache.
 *
 * Dropdown options has non-selectable display types. It is therefore not cheap to determine
 * the total number of actual selectable options as well as the position an option is in the
 * list of options - O(n) cost for each lookup.
 *
 * Given that we potentially have to make this determination on every single render pass, this
 * cache should provide a little bit of relief.
 */
var DropdownSizePosCache = /** @class */ (function () {
    function DropdownSizePosCache() {
        this._size = 0;
    }
    /**
     * Invalidates the cache and recalculate the size of selectable options.
     */
    DropdownSizePosCache.prototype.updateOptions = function (options) {
        var displayOnlyOptionsCache = [];
        var size = 0;
        for (var i = 0; i < options.length; i++) {
            if (options[i].itemType === DropdownMenuItemType.Divider || options[i].itemType === DropdownMenuItemType.Header) {
                displayOnlyOptionsCache.push(i);
            }
            else {
                size++;
            }
        }
        this._size = size;
        this._displayOnlyOptionsCache = displayOnlyOptionsCache;
    };
    Object.defineProperty(DropdownSizePosCache.prototype, "optionSetSize", {
        /**
         * The size of all the selectable options.
         */
        get: function () {
            return this._size;
        },
        enumerable: true,
        configurable: true
    });
    /**
     * Returns the position of this option element relative to the full set of selectable option elements.
     * Note: the first selectable element is position 1 in the set.
     * @param index The raw index of the option element.
     */
    DropdownSizePosCache.prototype.positionInSet = function (index) {
        if (index === undefined) {
            return undefined;
        }
        // we could possibly memoize this too but this should be good enough, most of the time (the expectation is that
        // when you have a lot of options, the selectable options will heavily dominate over the non-selectable options.
        var offset = 0;
        while (index > this._displayOnlyOptionsCache[offset]) {
            offset++;
        }
        if (this._displayOnlyOptionsCache[offset] === index) {
            throw new Error("Unexpected: Option at index " + index + " is not a selectable element.");
        }
        return index - offset + 1;
    };
    return DropdownSizePosCache;
}());
export { DropdownSizePosCache };
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