selector.js

/** !
 * Copyright (c) 2020, Matt Dunn
 *
 * @author Matt Dunn (https://matt-dunn.github.io/)
 * @licence MIT
 */

/**
 * Optimised selector - similar to reselect
 *
 * @method createSelector
 * @param {Function} [props]                                            Function that returns props or null for no props
 * @param {Function} [state]                                            Function that returns state or null for no state
 * @param {Function||Array.<Function>} selectors                        A function which returns immutable data (passing props, state) or another Selector (or an array of)
 * @param {Function} computeData                                        A function which computes state, passing the values in order of selectors
 * @returns {Object}                                                    Final computed state
 */
const createSelector = (props, state, selectors, computeData) => {
    const computeSelectors = Array.isArray(selectors) ? selectors : [selectors];

    let prevData = [],
        computedState;

    return () => {
        let hasChange = false;

        computeSelectors.map((selector, index) => {
            const currentData = selector(props && props(), state && state());

            if (currentData !== prevData[index]) {
                hasChange = true;

                prevData[index] = currentData;
            }
        });

        if (hasChange) {
            computedState = computeData(...prevData);
        }

        return computedState;
    };
};

export {createSelector};