var obj = {
  child: {}
}
obj.child = obj;
JSON.stringify(obj); // Uncaught TypeError: Converting circular structure to JSON

var arr = [];
arr[0] = arr;
JSON.stringify(arr); // Uncaught TypeError: Converting circular structure to JSON

var obj_1 = {
  childOne: {}
}
var obj_2 = {
  childTwo: {}
}
obj_1.childOne = obj_2;
obj_2.childTwo = obj_1;
JSON.stringify(obj_1); // Uncaught TypeError: Converting circular structure to JSON
JSON.stringify(obj_2); // Uncaught TypeError: Converting circular structure to JSON

var obj = {
  one: {
    childOne: {}
  },
  two: {
    childTwo: {}
  }	
}
obj.one.childOne = obj.two;
obj.two.childTwo = obj.one;
console.log(obj); // 可看到 obj 的结构中出现循环引用
JSON.stringfiy(obj); // Uncaught TypeError: Converting circular structure to JSON