Solution for the XOR list coding quiz

xorlist.js

// XOR list coding quiz solution

class Memory {
    constructor() {
        this.memory = {};
        this.pointerAccumulator = 100;
    }
    alloc() {
        const pointer = this.pointerAccumulator++;
        const obj = {
            pointer,
            value: {}
        };
        this.memory[pointer] = obj;
        return obj;
    }
    dereference(pointer) {
        if (!this.memory[pointer]) {
            throw new Error("dereferenced non-existence memory location:" + pointer);
        }
        return this.memory[pointer];
    }
}
const memory = new Memory();

class XorList {
    constructor(memory) {
        this.memory = memory;
        const headNode = memory.alloc();
        const tailNode = memory.alloc();
        headNode.value = {
            both: 0 ^ tailNode.pointer,
            payload: "HEAD",
        };
        tailNode.value = {
            both: 0 ^ headNode.pointer,
            payload: "TAIL",
        };

        this.headPointer = headNode.pointer;
        this.tailPointer = tailNode.pointer;
    }
    add(obj) {
        let newNodeRef = this.memory.alloc();
        newNodeRef.value.payload = obj;

        const tailNodeRef = this.memory.dereference(this.tailPointer);
        // pprev, prev(pprev^tail), tail(prev^0)
        // pprev, prev(pprev^new), new(prev^tail), tail(new^0)
        const tailPointer = this.tailPointer;
        const prevPointer = tailNodeRef.value.both;
        const prevNodeRef = this.memory.dereference(prevPointer);
        const pprevPointer = prevNodeRef.value.both ^ tailPointer;
        const newPointer = newNodeRef.pointer;

        prevNodeRef.value.both = pprevPointer ^ newPointer;
        newNodeRef.value.both = prevPointer ^ tailPointer;
        tailNodeRef.value.both = newPointer ^ 0;
    }
    get(index) {
        let prevPointer = 0;
        let currentPointer = this.headPointer;
        // prev, current(prev^next), next
        for (let i = 0; i <= index; i++) {
            const currentNodeRef = this.memory.dereference(currentPointer);
            let nextPointer = prevPointer ^ currentNodeRef.value.both;

            prevPointer = currentPointer;
            currentPointer = nextPointer;
        }
        return memory.dereference(currentPointer).value.payload;
    }
}
const ref = memory.alloc();
const list = new XorList(memory);
list.add("fish");
list.add("cod");
list.add("salmon");
console.log(list.get(0)); // fish
console.log(list.get(1)); // cod
console.log(list.get(2)); // salmon