Implentation of a hash table

hashing.js

function HashTable() {
  this.table = new Array(); 
  this.dupList = [];
}

HashTable.prototype.hashMethod = function(input){
  let strInput = input.toString();
  const encoder = 27; 
  let hashCode = 0; 
  for (let i = 0; i < strInput.length; i++) { 
    hashCode += encoder * hashCode + strInput.charCodeAt(i); 
  } 
  hashCode = hashCode % 150; 
  if (hashCode < 0) { 
    hashCode += 151; 
  } 
  return parseInt(hashCode); 
}

HashTable.prototype.getKey = function(value){
  return (`Key for ${value} --> ${HashTable.hashMethod(value)}`);
}

HashTable.prototype.storeData = function(data) { 
  let index = this.hashMethod(data); 
  if (this.table[index] === undefined){
    this.table[index] = [data];
  }
  else if (this.table[index] !== undefined){
    this.table[index].push(data);

    if (!this.dupList.includes(index)){
      this.dupList.push([index, data]);
    }
  }
}

HashTable.prototype.getAllItems = function() {  
  for (var i = 0; i < this.table.length; i++) {
    if (this.table[i] != undefined){ 
      console.log(`Index ${i}  contains ${this.table[i]}`); 
    } 
  } 
} 

HashTable.prototype.getDuplicates = function(array) {
  for(let i = 0; i<array.length; i++){
    this.storeData(array[i]);
  }
  this.dupList.map((pairs) =>{
    return (`${pairs[1]} occurs ${this.table[pairs[0]].length}`)    
  })


}

let arry = [3,5,5,3,3,"g","rt"]
let calc = new HashTable();
console.log (calc.getDuplicates(arry));