Hash Table (Hash Map) using Javascript

hashTable.js

function HashTable(){
  this.table = new Array(3)
  this.itemsLength = 0

  this.hashStringToInt = (str, tableSize) => {
    let hash = 13

    for (let i = 0; i < str.length; i++){
      hash = (13 * hash * str.charCodeAt(i)) 
    }

    return hash % tableSize
  }

  this.expandTable = () => {
    const loadFactor = this.itemsLength / this.table.length;
    if(loadFactor > 0.8){
    const newTable = new Array(this.table.length * 2);
    this.table.forEach(item => {
      if (item) {
        item.forEach(([key, value]) => {
          const idx = this.hashStringToInt(key, newTable.length);
          if (newTable[idx]) {
            newTable[idx].push([key, value]);
          } else {
            newTable[idx] = [[key, value]];
          }
        });
      }
    });
    this.table = newTable;
  }
  };

  this.addItem = (key,value) => {
    this.itemsLength++
      this.expandTable();
    const idx = this.hashStringToInt(key, this.table.length)

    if(this.table[idx]){
      this.table[idx].push([key, value])
    } else {
      this.table[idx] = [[key, value]]
    }
  }

  this.getItem = key => {
    const idx = this.hashStringToInt(key, this.table.length)

    if(!this.table[idx]){
      return undefined
    }

    return this.table[idx].find(x => x[0] === key)[1]
  }
}


const myTable = new HashTable();
myTable.addItem("firstName", "bob");
myTable.addItem("lastName", "tim");
myTable.addItem("1", "divine");
myTable.addItem("age", 5);
myTable.addItem("dob", "1/2/3");
// console.log(myTable.getItem("firstName"));
// console.log(myTable.getItem("lastName"));
// console.log(myTable.getItem("age"));
// console.log(myTable.getItem("dob"));

console.table(myTable.table)