LinkedList.js

// Single LinkedList
function LinkedList() {
    let length = 0;
    let head = null;

    let Node = function (element) {
        this.element = element;
        this.next = null;
    };

    this.size = function () {
        return length;
    };

    this.head = function () {
        return head;
    };

    this.add = function (element) {
        let node = new Node(element);
        if (head === null) {
            head = node;
        } else {
            currentNode = head;
            while (currentNode.next) {
                currentNode = currentNode.next;
            }
            currentNode.next = node;
        }
        length++;
    };

    this.remove = function (e) {
        if (head.element === e) {
            head = head.next;
            length--;
            return;
        } else {
            let currentNode = head;
            let prevNode;
            while (currentNode.next) {
                if (currentNode.element === e) {
                    break;
                }
                prevNode = currentNode;
                currentNode = currentNode.next;
            }
            prevNode.next = currentNode.next;
            return;
        }
    };

    this.isEmpty = function () {
        return length === 0;
    };

    this.indexOf = function (element) {
        let currentNode = head;
        for (let i = 0; i < length; i++) {
            if (currentNode.element === element) {
                return i;
            } else {
                currentNode = currentNode.next;
            }
        }
        return -1;
    };

    this.elementAt = function (index) {
        if (head === null) {
            return undefined;
        } else {
            let currentNode = head;
            let count = -1;
            while (currentNode) {
                count++;
                if (count === index) {
                    return currentNode.element;
                }
                currentNode = currentNode.next;
            }
            return undefined;
        }
    };

    this.removeAt = function (index) {
        if (head === null) {
            return null;
        } else if (index === 0) {
            let item = head;
            head = head.next;
            length--;
            return item.element;
        } else {
            let currentNode = head;
            let count = -1;
            let prevNode;
            while (currentNode) {
                count++;
                if (count === index) {
                    let item = currentNode;
                    prevNode.next = currentNode.next;
                    length--;
                    return item.element;
                }
                prevNode = currentNode;
                currentNode = currentNode.next;
            }
            return null;
        }
    };

    this.addAt = function (index, e) {
        let currentNode = head;
        let prevNode;
        let node = new Node(e);
        if (!currentNode && index > 0) return false;
        for (let i = 0; i < length + 1; i++) {
            if (index === 0) {
                node.next = currentNode;
                head = node;
                length++;
                return;
            }

            if (i === index) {
                prevNode.next = node;
                node.next = currentNode;
                length++;
                return;
            }

            if (!currentNode) return false;
            prevNode = currentNode;
            currentNode = currentNode.next;
        }
        return false;
    };

    this.reverse = function () {
        let currentNode = head;
        let savedNode;
        let prevNode;
        while (currentNode) {
            savedNode = currentNode.next;
            currentNode.next = prevNode;
            prevNode = currentNode;
            currentNode = savedNode;
        }
        head = prevNode;
        return head;
    };
}