Changing the value of an object property (illustrated using a basic linked list)

Question

Changing the value of an object property (illustrated using a basic linked list)

I am working on a JavaScript Link List implementation as a beginner, and I have written the following code:

var LinkList = function () {
  this.LinkedList = {
    "Head": {}
  };
};
LinkList.prototype = {
  insert: function (element) {
    var Node = this.head();
    while (Node.hasOwnProperty("Node")) {
      Node = this.next(Node);
    }
    Node["Node"] = {
      "element": element
    };
  },
  remove: function (element) {
    var Node = this.head();
    while (Node.element != element) {
      Node = this.next(Node);
    }
    delete Node.element;
    Node = Node.Node; //overwriting Node with Node.Node
  },
  next: function (Node) {
    return Node.Node;
  },
  head: function () {
    return this.LinkedList.Head;
  },
  getList: function () {
    return this.LinkedList;
  }
};

When I perform insertions using this code, everything works fine. For example:

var myList = new LinkList();
myList.insert(1);
myList.insert(5);
myList.insert(6);
myList.insert(2);

This results in a List structure like this:

    {
    "Head": {
        "Node": {
            "element": 1,
            "Node": {
                "element": 5,
                "Node": {
                    "element": 6,
                    "Node": {
                        "element": 2
                    }
                }
            }
        }
    }
}

However, when I try to remove an element, it doesn't give me the expected result. For example, if I remove the element 5:

myList.remove(5);

{
    "Head": {
        "Node": {
            "element": 1,
            "Node": {
                "Node": {
                    "element": 6,
                    "Node": {
                        "element": 2
                    }
                }
            }
        }
    }
}

I actually want the updated List to be like this:

{
    "Head": {
        "Node": {
            "element": 1,
            "Node": {
                "element": 6,
                "Node": {
                    "element": 2
                }
            }
        }
    }
}

Does anyone have any ideas on how to solve this issue? Thank you in advance.

javascript json data-structures

Answer 1

Answer №1

One reason for the issue is that when you assign Node = Node.Node, the next node is not being assigned as the current node. Instead, you are simply assigning Node.Node to the variable Node. As a result, you do not overwrite the current node but rather obtain only read privileges.

To overcome this and take advantage of passing references, you need to modify the property of the object that your variable is referencing. This way, you will have both read and modify privileges, so to speak.

Let me illustrate what happened in your code with a short example:

// Here we create an object
var foo = {}
  , bar;

// We assign the baz property carrying bam
foo.baz = 'bam';

// We reference foo.baz with bar
bar = foo.baz;

// Now, we expect that bar equals bam
console.log(bar); //bam

// However, in this operation, we merely assign the value boom to bar
// without modifying foo.baz
bar = 'boom';

// After modifying bar in this way, foo.baz remains as bam
console.log(bar); //boom
console.log(foo.baz) //bam?

Instead of this, I suggest using a simplified approach with a stripped-down version of the code:

var List = function () {
    this.head = {};
};
List.prototype = {
    insert: function (element) {
        var node = this.head;
        while (node.next) {
            node = node.next;
        }
        node.next = {
            "element": element
        };
    },
    remove: function (element) {

        // We start with head
        var node = this.head;

        // Basically, we assign node as the next node
        // so that we can operate on the next node instead of node itself
        // and modify its values

        // While the next node is not the one we are looking for
        while (node.next.element != element) {
            // Move to the next node
            node = node.next;
        }

        // Once we find our target, delete it
        delete node.next.element;

        // Rather than assigning to the variable node, we assign to a property
        // of the object that node is referencing
        node.next = node.next.next;
    }
};

By the way, remember to use descriptive names for your variables, properties, and other elements in your code.

Answer 2

One reason for the issue is that when you assign Node = Node.Node, the next node is not being assigned as the current node. Instead, you are simply assigning Node.Node to the variable Node. As a result, you do not overwrite the current node but rather obtain only read privileges.

To overcome this and take advantage of passing references, you need to modify the property of the object that your variable is referencing. This way, you will have both read and modify privileges, so to speak.

Let me illustrate what happened in your code with a short example:

// Here we create an object
var foo = {}
  , bar;

// We assign the baz property carrying bam
foo.baz = 'bam';

// We reference foo.baz with bar
bar = foo.baz;

// Now, we expect that bar equals bam
console.log(bar); //bam

// However, in this operation, we merely assign the value boom to bar
// without modifying foo.baz
bar = 'boom';

// After modifying bar in this way, foo.baz remains as bam
console.log(bar); //boom
console.log(foo.baz) //bam?

Instead of this, I suggest using a simplified approach with a stripped-down version of the code:

var List = function () {
    this.head = {};
};
List.prototype = {
    insert: function (element) {
        var node = this.head;
        while (node.next) {
            node = node.next;
        }
        node.next = {
            "element": element
        };
    },
    remove: function (element) {

        // We start with head
        var node = this.head;

        // Basically, we assign node as the next node
        // so that we can operate on the next node instead of node itself
        // and modify its values

        // While the next node is not the one we are looking for
        while (node.next.element != element) {
            // Move to the next node
            node = node.next;
        }

        // Once we find our target, delete it
        delete node.next.element;

        // Rather than assigning to the variable node, we assign to a property
        // of the object that node is referencing
        node.next = node.next.next;
    }
};

By the way, remember to use descriptive names for your variables, properties, and other elements in your code.

Changing the value of an object property (illustrated using a basic linked list)

Answer №1

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