SinglyLinkedList.js

class Node {
	constructor(value) {
		this.value = value;
		this.next = null;
	}
}

class SinglyLinkedList {
	constructor() {
		this.head = null;
		this.tail = null;
		this.length = 0;
	}

	push(value) {
		let node = new Node(value);
		if (!this.length) this.head = this.tail = node;
		else {
			this.tail.next = node;
			this.tail = node;
		}
		this.length++;

		return this;
	}

	pop() {
		if (!this.length) return;
		let current = this.head;
		let prev = current;
		if (this.length === 1) {
			this.head = this.tail = null;
		} else {
			while (current.next) {
				prev = current;
				current = current.next;
			}

			this.tail = prev;
			this.tail.next = null;
		}

		this.length--;
		return current;
	}

	get(index) {
		if (index < 0 || index >= this.length) return undefined;
		let current = this.head;

		for (let i = 0; i < this.length; i++) {
			if (i === index) break;
			current = current.next;
		}

		return current;
	}

	set(index, value) {
		let node = this.get(index);
		if (!node) return false;

		node.value = value;
		return true;
	}

	unshift(value) {
		if (this.length === 0) this.push(value);
		else {
			let node = new Node(value);
			node.next = this.head;
			this.head = node;
		}
		return this;
	}

	shift() {
		if (this.length === 0) return;
		if (this.length === 1) return this.pop();

		let removed = this.head;
		this.head = removed.next;
		removed.next = null;
		return removed;
	}

	insert(index, value) {
		if (index < 0 || index > this.length) return false;

		if (index === 0) return !!this.unshift(value);
		else if (index === this.length) return !!this.push(value);
		else {
			let node = new Node(value);
			let left = this.get(index - 1);
			let right = this.get(index);

			left.next = node;
			node.next = right;
			this.length++;
			return true;
		}
	}

	remove(index) {
		if (index < 0 || index >= this.length) return;

		if (index === 0) return this.shift();
		else if (index === this.length - 1) this.pop();
		else {
			let left = this.get(index - 1);
			let removed = left.next;
			let right = removed.next;

			left.next = right;
			this.length--;
			return removed;
		}
	}
}

let list = new SinglyLinkedList();
list.push(1); // 1
list.push(2); // 1 -> 2
list.push(5); // 1 -> 2 -> 5
list.push(13); // 1 -> 2 -> 5 -> 13
list.push(12); // 1 -> 2 -> 5 -> 13 -> 12
list.push(500); // 1 -> 2 -> 5 -> 13 -> 12 -> 500
list.pop(); // 1 -> 2 -> 5 -> 13 -> 12
list.pop(); // 1 -> 2 -> 5 -> 13
console.log(list.get(0).value); // 1
console.log(list.get(1).value); // 2
console.log(list.get(2).value); // 5
console.log(list.set(2, "Change 1")); // true
console.log(list.set(100, "Change 1")); // false
list.unshift("Unshifted in 1");
list.unshift("Unshifted in 2");
console.log(list.shift().value); // Unshifted in 2
console.log(list.insert(2, "Inserted")); // true
console.log(list.insert(5, "Inserted to the end")); // true
console.log(list.insert(200, "Inserted to invalid index")); // false
console.log(list);