Implementation of the hash table data structure in JavaScript.

javascript-hash-table.js

const hashFunction = (key, tableSize) => {
  // index we are going to return
  let index = 0

  // get list of characters in key string as an array
  let numChars = String(key)
  
  // assign numChars size to index to start
  index = numChars.length
  
  // loop through numChars and keep multiplying index by unicode of current character
  for (let i = 0; i < numChars.length; i++) {
    index *= numChars.charCodeAt(i)
  }

  // use mod to return a number between 0 and tableSize as index
  return index % tableSize
}

class HashTable {
  constructor (size) {
    this.table = new Array(size)
    this.size = this.table.length
  }

  has = key => {
    let index = hashFunction(key, this.size)

    // if value doesn't exist return false
    if (!this.table[index]) return false
    // else find the [key, value] pair with given key and return true if pair with key exists
    else {
      if (this.table[index].find(item => item[0] === key)) return true
      else return false
    }
  }

  get = key => {
    let index = hashFunction(key, this.size)

    // if key doesn't exist return null
    if (!this.table[index]) return null
    // else find the [key, value] pair with given key and return second element i.e. value part of [key, value] if exists
    // return null if doesn't
    else {
      if (this.table[index].find(item => item[0] === key)) {
        return this.table[index].find(item => item[0] === key)[1]
      }
      else return null
    }
  }  

  set = ([key, value]) => {
    let index = hashFunction(key, this.size)

    // if key doesn't exist at the index already, set an array with [key, value]
    if (!this.table[index]) this.table[index] = [[key, value]]
    // else push [key, value] to existing array
    else this.table[index].push([key, value])

  }

  remove = ([key, value]) => {
    let index = hashFunction(key, this.size)

    // if key doesn't exist at the index, return null
    if (!this.table[index]) this.table[index] = [[key, value]]
    // else find the [key, value] pair with given key and value  and remove it from index
    // return null if doesn't
    else {
      if (this.table[index].find(item => item[0] === key && item[1] === value)) {
        // [key, value] pair
        let item = this.table[index].find(item => item[0] === key && item[1] === value)

        // index of [key, value] pair
        let subIndex = this.table[index].indexOf(item)

        // remove item at subIndex
        this.table[index].splice(subIndex, 1)

        return [key, value]
      }
      else return null
    }
  }
}

// tests
const hashTable = new HashTable(40)

hashTable.set(['Abigail', '26'])
console.log(hashTable)
hashTable.set(['Tallie', '25'])
console.log(hashTable)
hashTable.set(['Jean', '28'])
console.log(hashTable)

console.log(hashTable.has('Abigail'))
console.log(hashTable.get('Abigail'))
console.log(hashTable.has('Lydia'))
console.log(hashTable.get('Lydia'))

console.log(hashTable.remove(['Abigail', '26']))
console.log(hashTable.has('Abigail'))

console.log(hashTable)