Used to find out whether an object contains a circular reference.

containsCircularPaths.js

/**
 * Used to find out whether an object contains a circular reference.
 * @param {*} rootObject The object we want to search within for circular references
 * @returns {bool} Returns true if a circular reference was found, otherwise returns false
 */
function containsCircularPaths(rootObject) {
  // Used to keep track of all the values the rootObject contains
  const traversedValues = new WeakSet();

  /**
   * 
   * @param {*} currentObj The current object we want to search within for circular references
   * @returns {true|undefined} Returns true if a circular reference was found, otherwise returns undefined
   */
  function _containsCircularPaths(currentObj) {
    // If we already saw this object
    // the rootObject contains a circular reference
    // and we can stop looking any further
    if (traversedValues.has(currentObj)) {
      return true;
    }

    // Only Objects and things which inherit from Objects can contain circular references
    // I.E. string/number/boolean/template literals can not contain circular references
    if (currentObj instanceof Object) {
      traversedValues.add(currentObj); 
      // Loop through all the values of the current object and 
      for (const key in currentObj) {
        const value = currentObj[key];
        // No need to recurse on every value because only things which inherit 
        // from Objects can contain circular references
        if (value instanceof Object) {
          if (_containsCircularPaths(value)) {
            return true;
          }
        }
      }
    }
  }

  // _containsCircularPaths returns true or undefined.
  // By using Boolean we convert the undefined into false.
  return Boolean(_containsCircularPaths(rootObject));
}