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JavaScript

Posted by de forbe
de forbe
76 Points

Object prototype not supporting arrow function

I am working on Linked List in JavaScript. When I add prototype to my Link List Object with arrow function it doesn't work but when I do the same task with normal function It works fine. This is my code:

function LinkedList() {
  this.head = null;
  this.tail = null;
}
function Node(value, head, tail) {
  this.value = value;
  this.head = head;
  this.tail = tail;
}
LinkedList.prototype.addToHead = function(value) {
  node = new Node(value, this.head, null);
  if (this.head) this.head.tail = node;
  else this.tail = node;
  this.head = node;
}
// LinkedList.prototype.addToHead = value => {
//   node = new Node(value, this.head, null);
//   if (this.head) this.head.tail = node;
//   else this.tail = node;
//   this.head = node;
// }
const list = new LinkedList();
list.addToHead(100)
console.dir(list)

Output with normal function: 

LinkedList {
  head: Node { value: 100, head: null, tail: null },
  tail: Node { value: 100, head: null, tail: null } }

Output when i un-comment that arrow functioned code and comment that normal functioned code:

LinkedList { head: null, tail: null }

1 Answer

Amber Cyr
Amber Cyr
19,699 Points
Amber Cyr
Amber Cyr
19,699 Points

unfortunately, you can not use the arrow syntax in some instances, prototype declaration being one of them. This is because arrow functions will bind to the context you declared it in. This case it is binding to the value within your LinkedList.prototype.addToHead and not creating the .addToHead method. I have also provided a link that may be helpful to you as well.

de forbe
de forbe
76 Points

Thanks for your help mam.