At the JSON site it says
JSON does not support cyclic data structures, so be careful to not give cyclical structures to the JSON stringifier.
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CYCLE: A situation in which you return to the same place where you started.
CYCLIC DATA STRUCTURE: A data structure in which such situation might arise. For example graph,linked list (singly/doubly), dequeue, etc.
A linked list node in JS is implemented as:
function Node(data){
this.data = data;
this.next = null;
}
Now I create two such nodes as shown below:
var node1 = new Node(10);
var node2 = new Node(20);
And link them to form a cycle.
node1.next = node2;
node2.next = node1;
The following traversal code will enter an infinite loop which shows the existence of a cycle.
node = node1;
while(node!==null){
print(node.data);
node = node.next;
}