moodle/lib/amd/src/utils.js

// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**
 * Utility functions.
 *
 * @module core/utils
 * @copyright  2019 Ryan Wyllie <ryan@moodle.com>
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

import Pending from 'core/pending';
import jQuery from 'jquery';

 /**
  * Create a wrapper function to throttle the execution of the given
  *
  * function to at most once every specified period.
  *
  * If the function is attempted to be executed while it's in cooldown
  * (during the wait period) then it'll immediately execute again as
  * soon as the cooldown is over.
  *
  * @method
  * @param {Function} func The function to throttle
  * @param {Number} wait The number of milliseconds to wait between executions
  * @return {Function}
  */
export const throttle = (func, wait) => {
    let onCooldown = false;
    let runAgain = null;
    const run = function(...args) {
        if (runAgain === null) {
            // This is the first time the function has been called.
            runAgain = false;
        } else {
            // This function has been called a second time during the wait period
            // so re-run it once the wait period is over.
            runAgain = true;
        }

        if (onCooldown) {
            // Function has already run for this wait period.
            return;
        }

        func.apply(this, args);
        onCooldown = true;

        setTimeout(() => {
            const recurse = runAgain;
            onCooldown = false;
            runAgain = null;

            if (recurse) {
                run(args);
            }
        }, wait);
    };

    return run;
};

/**
 * @property {Map} debounceMap A map of functions to their debounced pending promises.
 */
const debounceMap = new Map();

/**
 * Create a wrapper function to debounce the execution of the given
 * function. Each attempt to execute the function will reset the cooldown
 * period.
 *
 * @method
 * @param {Function} func The function to debounce
 * @param {Number} wait The number of milliseconds to wait after the final attempt to execute
 * @param {Object} [options]
 * @param {boolean} [options.pending=false] Whether to wrap the debounced method in a pending promise
 * @param {boolean} [options.cancel=false] Whether to add a cancel method to the debounced function
 * @return {Function}
 */
export const debounce = (
    func,
    wait,
    {
        pending = false,
        cancel = false,
    } = {},
) => {
    let timeout = null;

    const returnedFunction = (...args) => {
        if (pending && !debounceMap.has(returnedFunction)) {
            debounceMap.set(returnedFunction, new Pending('core/utils:debounce'));
        }
        clearTimeout(timeout);
        timeout = setTimeout(async () => {
            // Get the current pending promise and immediately empty it.
            // This is important to allow the function to be debounced again as soon as possible.
            // We do not resolve it until later - but that's fine because the promise is appropriately scoped.
            const pendingPromise = debounceMap.get(returnedFunction);
            debounceMap.delete(returnedFunction);

            // Allow the debounced function to return a Promise.
            // This ensures that Behat will not continue until the function has finished executing.
            await func.apply(this, args);

            // Resolve the pending promise if it exists.
            pendingPromise?.resolve();
        }, wait);
    };

    if (cancel) {
        returnedFunction.cancel = () => {
            const pendingPromise = debounceMap.get(returnedFunction);
            pendingPromise?.resolve();
            clearTimeout(timeout);
        };
    }

    return returnedFunction;
};

/**
 * Normalise the provided component such that '', 'moodle', and 'core' are treated consistently.
 *
 * @param   {String} component
 * @returns {String}
 */
export const getNormalisedComponent = (component) => {
    if (component) {
        if (component !== 'moodle' && component !== 'core') {
            return component;
        }
    }

    return 'core';
};

/**
 * Wrap a Native Promise in a jQuery Whenable for b/c.
 *
 * @param {*} promise
 * @returns {jQuery}
 */
export const wrapPromiseInWhenable = (promise) => jQuery.when(promise);