Bubble sort method in JavaScript

Question

In my TaskList class, I have a method called sortByWhenDue which is supposed to sort the Task objects in the _tasks attribute by the dates and times they are due (ie the Date object stored in the _whenDue attribute) from earliest to latest. However, when I try to use it, I get the error message Uncaught TypeError: Cannot read properties of undefined (reading '_whenDue') . Does anyone know what I should do about this? THanks.

class Task
{
    /**
     * @param {String} taskName a short description of the task
     * @param {String} category the category of the task
     * @param {Date} whenDue when the task is due
     */
    constructor(taskName, category, whenDue) {
        this._taskName = taskName;
        this._category = category;
        this._whenDue = whenDue;
    }

    get taskName() {
        return this._taskName;
    }

    get category() {
        return this._category;
    }

    get whenDue() {
        return this._whenDue;
    }

    set taskName(newTaskName) {
        if (typeof newTaskName === 'string') {
            this._taskName = newTaskName;
        }
    }

    set category(newCategory) {
        if (typeof newCategory === 'string') {
            this._category = newCategory;
        }
    }

    set whenDue(newWhenDue) {
        if (typeof newWhenDue === 'object') {
            this._whenDue = newWhenDue;
        }
    }

    fromData(data) {
        this._taskName = data._taskName;
        this._category = data._category;
        this._whenDue = data._whenDue;
    }
}

class TaskList
{
    constructor() {
        this._tasks = [];
    }

    get tasks() {
        return this._tasks;
    }

    addTask(task) {
        if (typeof(task) === 'object') {
            this._tasks.push(task);
        }
    }

    getTask(taskIndex) {
        return this._tasks[taskIndex];
    }

    fromData(data) {
        this._tasks = [];
        for (let i = 0; i < data._tasks.length; i++) {
            let tempName = data._tasks[i]._taskName;
            let tempCategory = data._tasks[i]._category;
            let tempWhenDue = new Date(data._tasks[i]._whenDue);
            let tempTask = new Task(tempName, tempCategory, tempWhenDue);
            this._tasks.push(tempTask);
        }
    }

    sortByWhenDue() {
        do { 
            let swapped = false;
            for (let i = 0; i < this._tasks.length; i++) {
                if (this._tasks[i]._whenDue > this._tasks[i+1]._whenDue) {
                    let temp = this._tasks[i+1];
                    this._tasks[i+1] = this._tasks[i];
                    this._tasks[i] = temp;
                    swapped = true;
                }
            }
        } while (swapped);
    }
}

Answer 1

The this._tasks[i+1] is the problem. If you reach the end of for loop your code tries to access an index which does not exists. So undefined is returned and your code tries to get _whenDue from undefined .