Hash Table in javascript

HashTable.js

function _hash(key, size) {
  key = key.toString();
  var hash = 5381;
  for(var i in key){
    var c = key[i];
    hash = ((hash << 5) + hash) + c.charCodeAt(0); /* hash * 33 + c */
  }
  return hash % size;
}

function _loadFactor(elements, bucketsSize) {
  return elements / (bucketsSize*1.0);
}

function _addEntry(idx, entry, buckets) {
  if(buckets[idx] != null){
    buckets[idx].push(entry);
  } else {
    buckets[idx] = [entry];
  }
}

function _findEntryIn(bucket, key){
  if(bucket != null) {
    var found = null;
    var idx = null;
    bucket.some(function(entry, i){
      if(entry.key == key){
        found = entry;
        idx = i;
        return true;
      }
    });
    return [found, idx];
  }
  return null;
}

function _rehash(ht, newBucketsSize){
  var newBuckets = Array(newBucketsSize);

  ht.buckets.forEach(function(bucket){
    if(bucket != null){
      bucket.forEach(function(entry){
        var idx = _hash(entry.key, newBuckets.length);
        _addEntry(idx, entry, newBuckets);
      });
    }
  });
  ht.buckets = newBuckets;
}

function BucketEntry(key, val) {
  this.key = key;
  this.val = val;
}

function HashTable(n) {
  n = typeof n !== 'undefined' ? n*10 : 1000;

  this.buckets = new Array(n);
  this.size = 0;
}

HashTable.prototype.put = function(key, val){
  var idx = _hash(key, this.buckets.length);
  var entry = new BucketEntry(key, val);

  _addEntry(idx, entry, this.buckets);
  this.size++;

  if(_loadFactor(this.size, this.buckets.length) > 0.75){
    _rehash(this, this.buckets.length*2);
  }
  return val;
};

HashTable.prototype.get = function(key){
  var idx    = _hash(key, this.buckets.length);
  var entry  = _findEntryIn(this.buckets[idx], key)[0];

  if(entry != null){
    return entry.val;
  }
  return null;
};

HashTable.prototype.del = function(key){
  var idx    = _hash(key, this.buckets.length);
  var bucket = this.buckets[idx];
  var res    = _findEntryIn(bucket, key);
  var entry  = res[0];

  if(entry != null) {
    var pos = res[1];
    var removed = bucket.splice(pos, 1)[0].val;
    this.size--;

    if(_loadFactor(this.size, this.buckets.length) < 0.1){
      _rehash(this, this.buckets.length/2);
    }
    return removed;
  }
  return false;
};

HashTable.prototype.contains = function(key){
  var idx    = _hash(key, this.buckets.length);
  var entry  = _findEntryIn(this.buckets[idx], key)[0];

  if(entry != null){
    return true;
  }
  return false;
};


module.exports = HashTable;