Implement a removeCycle function

Apr 04, 2024

In JavaScript, a cycle in an object occurs when there are circular references within the object’s structure. Circular references mean that an object references itself directly or indirectly through a chain of references.

1. Basic implementaion

Implement a removeCycle function which can take an object with circular references and delete them. It can mutate the original object.

function removeCycle(inputObj) {
  const visited = new WeakSet([inputObj]);

  for (const key in inputObj) {
    // only for non inhertied keys
    if (Object.hasOwn(inputObj, key)) {
      const value = inputObj[key];

      if (typeof value === 'object' && value != null) {
        if (visited.has(value)) {
          delete inputObj[key];
        }

        visited.add(value);
      }
    }
  }
}

// Usage
const obj = {
  a: 1,
  b: 2,
  d: null
};

// create a cyclic reference
obj.c = obj;

removeCycle(obj);

/**
 * Yields:
 * {
    "a": 1,
    "b": 2,
    "d": null
  }
 */
console.log(obj);