I am eager to incorporate a hashtable in my JavaScript code, but unfortunately, I am encountering an unexpected

Question

I am eager to incorporate a hashtable in my JavaScript code, but unfortunately, I am encountering an unexpected

function MyHashTable(){
    var totalSize = 0;
    var dataEntry = new Object();
    this.addItem = function(key, value){
        if(!isKeyPresent(key)){
            totalSize++;
        }
        dataEntry[key] = value;
    }

    this.fetchValue = function(key){
        return isKeyPresent(key) ? dataEntry[key] : null;
    }

    this.deleteItem = function(key){
        if (isKeyPresent(key) && delete dataEntry[key]) {
            totalSize--;
        }
    }

    this.isKeyPresent = function(key){
        return (key in dataEntry);
    }

    this.isValuePresent = function(value){
        for(var prop in dataEntry){
            if(dataEntry[prop] == value){
                return true;
            }
        }
        return false;
    }

    this.getAllValues = function(){
        var values = new Array();
        for(var prop in dataEntry){
            values.push(dataEntry[prop]);
        }
        return values;
    }

    this.getAllKeys = function(){
        var keys = new Array();
        for(var prop in dataEntry){
            keys.push(prop);
        }
        return keys;
    }

    this.getSize = function(){
        return totalSize;
    }

    this.clearAll = function(){
        totalSize = 0;
        dataEntry = new Object();
    }
}

var myHashTableExample = new MyHashTable();
myHashTableExample.addItem('name', 'John');

I am trying to create a custom hash table in JavaScript but when I run a test, I encounter an error message:

Uncaught ReferenceError: containsKey is not defined at MyHashTable.addItem (:8:3) at :64:10

javascript hashtable

Answer 1

Answer №1

The issue at hand pertains to the concept of scope in JavaScript. The problem arises when the JavaScript interpreter is uncertain about which containsKey function to refer to within the HashTable class.

It is crucial to specify the scope when calling functions within a class by using "this". For instance, containsKey should be called as this.containsKey(key) to ensure that the interpreter understands that you are referring to the class scope rather than the local scope.

Similarly, it is advisable to prefix variables with "this" to indicate class scope. For example, instead of using size++, it is recommended to utilize this.size++. Failing to use "this" could result in the interpreter treating the function or variable as local to the function itself.

Here's a revised version of your add() function:

this.add = function(key, value){
        if(!this.containsKey(key)){
            this.size++;
        }
        this.entry[key] = value;
    }

Additionally, consider using an array for "entry" and accessing its size as this.entry.size instead of manually managing size.

To simplify the hashmap implementation, you can create two arrays within the object for keys and values, allowing you to leverage built-in JavaScript array functions for more efficiency. Each key and value will share the same index, ensuring easy correlation between them. Here is a modified example:

function HashTable() {
  this.keys = new Array();
  this.values = new Array();

  this.add = function(key, value) {

    if (this.containsKey(key)) {
      var index = this.keys.indexOf(key);
      this.values[index] = value;
    } else {
      this.keys.push(key);
      this.values.push(value);
    }
  }

  this.containsKey = function(key) {
    return this.keys.includes(key);
  }

  // More functions for handling keys, values, and size

}

// Additional code snippets for utilizing the HashTable class comes here.

Answer 2

The issue at hand pertains to the concept of scope in JavaScript. The problem arises when the JavaScript interpreter is uncertain about which containsKey function to refer to within the HashTable class.

It is crucial to specify the scope when calling functions within a class by using "this". For instance, containsKey should be called as this.containsKey(key) to ensure that the interpreter understands that you are referring to the class scope rather than the local scope.

Similarly, it is advisable to prefix variables with "this" to indicate class scope. For example, instead of using size++, it is recommended to utilize this.size++. Failing to use "this" could result in the interpreter treating the function or variable as local to the function itself.

Here's a revised version of your add() function:

this.add = function(key, value){
        if(!this.containsKey(key)){
            this.size++;
        }
        this.entry[key] = value;
    }

Additionally, consider using an array for "entry" and accessing its size as this.entry.size instead of manually managing size.

To simplify the hashmap implementation, you can create two arrays within the object for keys and values, allowing you to leverage built-in JavaScript array functions for more efficiency. Each key and value will share the same index, ensuring easy correlation between them. Here is a modified example:

function HashTable() {
  this.keys = new Array();
  this.values = new Array();

  this.add = function(key, value) {

    if (this.containsKey(key)) {
      var index = this.keys.indexOf(key);
      this.values[index] = value;
    } else {
      this.keys.push(key);
      this.values.push(value);
    }
  }

  this.containsKey = function(key) {
    return this.keys.includes(key);
  }

  // More functions for handling keys, values, and size

}

// Additional code snippets for utilizing the HashTable class comes here.

Answer 3

Answer №2

Opt for using this.containsKey instead of containsKey since containsKey is a method specific to the object created by HashTable and should be referenced using this.

function HashTable(){
    var size = 0;
    var entry = new Object();
    
    this.containsValue = function(value){
        for(var prop in entry){
            if(entry[prop] == value){
                return true;
            }
        }
        return false;
    }
    
    this.add = function(key,value){
        if(!this.containsKey(key)){
            size++;
        }
        entry[key] = value;
    }

this.getValue = function(key){
    return this.containsKey(key)?entry[key]:null;
}

this.remove = function(key){
    if (this.containsKey(key) && delete entry[key]) {
        size--;
    }
}

this.containsKey = function(key){
    return (key in entry);
}


//get all values
    this.getValues = function(){
        var values = new Array();
        for(var prop in entry){
            values.push(entry[prop]);
        }
        return values;
    }
//get all keys
    this.getKeys = function(){
        var keys = new Array();
        for(var prop in entry){
            values.push(prop);
        }
        return keys;
    }
this.getSize = function(){
    return size;
}

this.clear = function(){
    size = 0;
    entry = new Object;//???????????????????
}
}

var hashtest = new HashTable(); hashtest.add('name','LiMing');
console.log(hashtest.getValues())

One can enhance code structure using ES6:

class HashTable {
  constructor() {
    this.size = 0;
    this.entry = new Object();
  }
  
  containsValue(value) {
    for(var prop in entry){
      if(this.entry[prop] == value){
        return true;
      }
    }
    return false;
  }
  
  add(key,value) {
    if(!this.containsKey(key)){
      this.size++;
    }
    this.entry[key] = value;
  }
  
  getValue(key) {
    return this.containsKey(key) ? this.entry[key] : null;
  }
  
  remove(key) {
    if (this.containsKey(key) && delete this.entry[key]) {
      size--;
    }
  }
  
  containsKey(key) {
    return (key in this.entry);
  }
  
  //get all values
  getValues() {
    var values = new Array();
    for(var prop in this.entry){
      values.push(this.entry[prop]);
    }
    return values;
  }
  
  //get all keys
  getKeys() {
    var keys = new Array();
    for(var prop in this.entry){
      values.push(prop);
    }
    return keys;
  }
  
  getSize() {
    return this.size;
  }
  
  clear() {
    this.size = 0;
    this.entry = new Object();//???????????????????
  }
  
}


var hashtest = new HashTable(); hashtest.add('name','LiMing');
console.log(hashtest.getValues())

Answer 4

Opt for using this.containsKey instead of containsKey since containsKey is a method specific to the object created by HashTable and should be referenced using this.

function HashTable(){
    var size = 0;
    var entry = new Object();
    
    this.containsValue = function(value){
        for(var prop in entry){
            if(entry[prop] == value){
                return true;
            }
        }
        return false;
    }
    
    this.add = function(key,value){
        if(!this.containsKey(key)){
            size++;
        }
        entry[key] = value;
    }

this.getValue = function(key){
    return this.containsKey(key)?entry[key]:null;
}

this.remove = function(key){
    if (this.containsKey(key) && delete entry[key]) {
        size--;
    }
}

this.containsKey = function(key){
    return (key in entry);
}


//get all values
    this.getValues = function(){
        var values = new Array();
        for(var prop in entry){
            values.push(entry[prop]);
        }
        return values;
    }
//get all keys
    this.getKeys = function(){
        var keys = new Array();
        for(var prop in entry){
            values.push(prop);
        }
        return keys;
    }
this.getSize = function(){
    return size;
}

this.clear = function(){
    size = 0;
    entry = new Object;//???????????????????
}
}

var hashtest = new HashTable(); hashtest.add('name','LiMing');
console.log(hashtest.getValues())

One can enhance code structure using ES6:

class HashTable {
  constructor() {
    this.size = 0;
    this.entry = new Object();
  }
  
  containsValue(value) {
    for(var prop in entry){
      if(this.entry[prop] == value){
        return true;
      }
    }
    return false;
  }
  
  add(key,value) {
    if(!this.containsKey(key)){
      this.size++;
    }
    this.entry[key] = value;
  }
  
  getValue(key) {
    return this.containsKey(key) ? this.entry[key] : null;
  }
  
  remove(key) {
    if (this.containsKey(key) && delete this.entry[key]) {
      size--;
    }
  }
  
  containsKey(key) {
    return (key in this.entry);
  }
  
  //get all values
  getValues() {
    var values = new Array();
    for(var prop in this.entry){
      values.push(this.entry[prop]);
    }
    return values;
  }
  
  //get all keys
  getKeys() {
    var keys = new Array();
    for(var prop in this.entry){
      values.push(prop);
    }
    return keys;
  }
  
  getSize() {
    return this.size;
  }
  
  clear() {
    this.size = 0;
    this.entry = new Object();//???????????????????
  }
  
}


var hashtest = new HashTable(); hashtest.add('name','LiMing');
console.log(hashtest.getValues())

I am eager to incorporate a hashtable in my JavaScript code, but unfortunately, I am encountering an unexpected

Answer №1

Answer №2

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