Hash Map Implementation

HashMap.js

class HashMap {
  constructor(capacity) {
    this.length = 0;
    this._slots = [];
    this.capacity = capacity || 8;
    this.deleted = 0;
  };

  set(key, value) {
    const loadRatio = (this.length + this.deleted + 1) / this.capacity;
    if (loadRatio > this.MAX_LOAD_RATIO) {
      this._resize(this.capacity * this.SIZE_RATIO)
    }

    const index = this._findSlot(key);
    this._slots[index] = {
      key,
      value,
      deleted: false
    }
    this.length++;
  }

  get(key) {
    const index = this._findSlot(key);
    if (index === undefined) {
      throw new Error('key error');
    }
    return this._slots[index].value;
  }

  remove(key) {
    const index = this._findSlot(key);
    const slot = this._slots[index];
    if (slot === undefined) {
      throw new Error('key error: not found');
    }
    slot.deleted = true; // soft delete
    this.length--;
    this.deleted++;
  }

  _hashString(string) {
    var hash = 5381;
    for (var i=0; i<string.length; i++) {
        hash = (hash << 5) + hash + string.charCodeAt(i);
        hash = hash & hash;
    }
    return hash >>> 0;
  }

  _resize(size) {
    let oldSlots = this._slots;
    this.length = 0;
    this.capacity = size;
    this.deleted = 0;
    this._slots = [];
    for (let i = 0; i < oldSlots.length; i += 1) {
      const slot = oldSlots[i];
      if (slot !== undefined) {
        this.set(slot.key, slot.value);
      }
    }
  }

  _findSlot(key) {
    const hash = this._hashString(key);
    const start = hash % this.capacity;
    for (let i = start; i < start + this.capacity; i += 1) {
      let index = i % this.capacity;
      let slot = this._slots[index];
      if (slot === undefined || (slot.key == key && !slot.deleted) ) {
        return index;
      }
    }
  }
}

let map = new HashMap(7);
map.MAX_LOAD_RATIO = 0.9;
map.SIZE_RATIO = 3;

map.set('New York', 'Albany');
map.set('Massachussetts', 'Boston');
map.set('Florida', 'Tallahassee');

console.log(map);
console.log('Capital of Florida is: ', map.get('Florida'));
console.log('Capital of Massachussetts is: ', map.get('Massachussetts'));
console.log('Removing New York.....');
map.remove('New York');
console.log('Map updated view......');
console.log(map);