javascript 中的突变？

Question

In the below code size2() method working fine.But in size1() it is mutating the object and making it null.why such behavior is not happening in size2() ?

class Node {
    constructor(data, next = null) {
        this.data = data;
        this.next = next;
    }
}

class LinkedList {
    constructor() {
        this.head = null;
    }

    insert(data) {
        this.head = new Node(data, this.head);
    }

    size1() {
        var counter = 0;
        while (this.head) {
            counter++;
            this.head = this.head.next;
        }
        return counter;
    }

    size2() {
        var counter = 0;
        var node = this.head;
        while (node) {
            counter++;
            node = node.next;
        }
        return counter;
    }
}
var list = new LinkedList();
list.insert(35);

console.log(list);
console.log(list.size2());

To me both the method looks same. Is there any subtle difference in those methods?

Answer 1

In size2() , you are not mutating this.head because you first copy the reference in a local variable. Since in the while loop you are mutating the local node = node.next starting here node and this.head are not linked any more. It's the eternal Value/Reference pitfall .

Here is a related article .