Function decycle

libs/common/src/utils/json.utils.ts:6–75

(object: unknown, refKey = '__ref__')

// Normally schemas will be decycled on the server and retrocycled on the client.

export function decycle(object: unknown, refKey = '__ref__'): unknown {
  // Make a deep copy of an object or array, assuring that there is at most
  // one instance of each object or array in the resulting structure. The
  // duplicate references (which might be forming cycles) are replaced with
  // an object of the form {"__ref__": PATH} where the PATH is a JSONPath string that locates the first occurance.

  // So,
  //      let a = [];
  //      a[0] = a;
  //      return JSON.stringify(JSON.decycle(a));

  // produces the string '[{"__ref__":"$"}]'.

  // JSONPath is used to locate the unique object. $ indicates the top level of
  // the object or array. [NUMBER] or [STRING] indicates a child element or
  // property.

  const objects = new WeakMap() // object to path mappings

  return (function derez(value: unknown, path: string): unknown {
    // The derez function recurses through the object, producing the deep copy.

    let oldPath // The path of an earlier occurance of value
    let nu // The new object or array

    // typeof null === "object", so go on if this value is really an object but not
    // one of the weird builtin objects.

    if (
      typeof value === 'object' &&
      value !== null &&
      !(value instanceof Boolean) &&
      !(value instanceof Date) &&
      !(value instanceof Number) &&
      !(value instanceof RegExp) &&
      !(value instanceof String)
    ) {
      // If the value is an object or array, look to see if we have already
      // encountered it. If so, return a {"__ref__":PATH} object. This uses an
      // ES6 WeakMap.

      oldPath = objects.get(value)
      if (oldPath !== undefined) {
        return { [refKey]: oldPath }
      }

      // Otherwise, accumulate the unique value and its path.

      objects.set(value, path)

      // If it is an array, replicate the array.

      if (Array.isArray(value)) {
        nu = []
        value.forEach(function (element, i) {
          nu[i] = derez(element, `${path}[${i}]`)
        })
      } else {