circ-json/app/src/circJson.ts

Json (=readable) inspired serializer.

// This is a port of json-decycle. It has a few bug fixes and is in ts.

const isObject = (value: any) => typeof value === 'object'
&& value != null
&& !(value instanceof Boolean)
&& !(value instanceof Date)
&& !(value instanceof Number)
&& !(value instanceof RegExp)
&& !(value instanceof String)


const toPointer = (parts: string[]) => '#' + parts.map(part => String(part).replace(/~/g, '~0').replace(/\//g, '~1')).join('/')

const sym = Symbol('$ref')

export function decycle() {
 const paths = new WeakMap()

 return function replacer(key: string | symbol, value: any) {
   if (key === '$ref' && (typeof value === "string" || (value instanceof String && !value[sym])) && value.startsWith("#")) return "#" + value
   if (isObject(value)) {
     const seen = paths.has(value)

     if (seen) {
       const $ref = new String(toPointer(paths.get(value)))
       $ref[sym] = true
       return { $ref }
     } else {
       paths.set(value, [...paths.get(this) ?? [], key])
     }
   }

   return value
 }
}


export function retrocycle() {
  const parents = new WeakMap()
  const keys = new WeakMap()
  const refs = new Set()

  /**
   * @param {{ $ref: string }} ref
   * @this object
   */
  function dereference(ref) {
    const parts = ref.$ref.slice(1).split('/')
    let key, parent, value = this

    for (var i = 0; i < parts.length; i++) {
      key = parts[i].replace(/~1/g, '/').replace(/~0/g, '~')
      value = value[key]
    }

    parent = parents.get(ref)
    parent[keys.get(ref)] = value
  }

  return function reviver(key: string | symbol, value: any) {
    if (key === '$ref' && typeof value === "string") {
      if (value.startsWith("##")) return value.slice(1)
      else if (value.startsWith("#")) {
        refs.add(this)
        return value
      }
    } 
    if (isObject(value)) {
      var isRoot = key === '' && Object.keys(this).length === 1
      if (isRoot) {
        refs.forEach(dereference, this)
      } else {
        parents.set(value, this)
        keys.set(value, key)
      }
    }

    return value
  }
}



export function parse(str: string) {
 if (str === undefined) return undefined
 return JSON.parse(str, retrocycle())
}

export function stringify(obj: any, space?: string | number) {
 return JSON.stringify(obj, decycle(), space)
}