Serializing object that contains cyclic object value

I have an object (parse tree) that contains child nodes which are references to other nodes.

I'd like to serialize this object, using JSON.stringify(), but I get

TypeError: cyclic object value

because of the constructs I mentioned.

How could I work around this? It does not matter to me whether these references to other nodes are represented or not in the serialized object.

On the other hand, removing these properties from the object when they are being created seems tedious and I wouldn't want to make changes to the parser (narcissus).

Answers:

Answer

Use the second parameter of stringify, the replacer function, to exclude already serialized objects:

var seen = [];

JSON.stringify(obj, function(key, val) {
   if (val != null && typeof val == "object") {
        if (seen.indexOf(val) >= 0) {
            return;
        }
        seen.push(val);
    }
    return val;
});

http://jsfiddle.net/mH6cJ/38/

As correctly pointed out in other comments, this code removes every "seen" object, not only "recursive" ones.

For example, for:

a = {x:1};
obj = [a, a];

the result will be incorrect. If your structure is like this, you might want to use Crockford's decycle or this (simpler) function which just replaces recursive references with nulls:

function decycle(obj, stack = []) {
    if (!obj || typeof obj !== 'object')
        return obj;
    
    if (stack.includes(obj))
        return null;

    let s = stack.concat([obj]);

    return Array.isArray(obj)
        ? obj.map(x => decycle(x, s))
        : Object.fromEntries(
            Object.entries(obj)
                .map(([k, v]) => [k, decycle(v, s)]));
}

//

let a = {b: [1, 2, 3]}
a.b.push(a);

console.log(JSON.stringify(decycle(a)))

Answer

I've created an GitHub Gist which is able to detect cyclic structures and also de- and encodes them: https://gist.github.com/Hoff97/9842228

To transform just use JSONE.stringify/JSONE.parse. It also de- and encodes functions. If you want to disable this just remove lines 32-48 and 61-85.

var strg = JSONE.stringify(cyclicObject);
var cycObject = JSONE.parse(strg);

You can find an example fiddle here:

http://jsfiddle.net/hoff97/7UYd4/

Answer

much saver and it shows where an cycle object was.

<script>
var jsonify=function(o){
    var seen=[];
    var jso=JSON.stringify(o, function(k,v){
        if (typeof v =='object') {
            if ( !seen.indexOf(v) ) { return '__cycle__'; }
            seen.push(v);
        } return v;
    });
    return jso;
};
var obj={
    g:{
        d:[2,5],
        j:2
    },
    e:10
};
obj.someloopshere = [
    obj.g,
    obj,
    { a: [ obj.e, obj ] }
];
console.log('jsonify=',jsonify(obj));
</script>

produces

jsonify = {"g":{"d":[2,5],"j":2},"e":10,"someloopshere":[{"d":[2,5],"j":2},"__cycle__",{"a":[10,"__cycle__"]}]}
Answer
function stringifyObject ( obj ) {
  if ( _.isArray( obj ) || !_.isObject( obj ) ) {
    return obj.toString()
  }
  var seen = [];
  return JSON.stringify(
    obj,
    function( key, val ) {
      if (val != null && typeof val == "object") {
        if ( seen.indexOf( val ) >= 0 )
          return
          seen.push( val )
          }
      return val
    }
  );
}

A precondition was missing, otherwise the integer values in array objects are truncated, i.e. [[ 08.11.2014 12:30:13, 1095 ]] 1095 gets reduced to 095.

Answer

I create too a github project that can serialize cyclic object and restore the class if you save it in the serializename attribute like a String

var d={}
var a = {b:25,c:6,enfant:d};
d.papa=a;
var b = serializeObjet(a);
assert.equal(  b, "{0:{b:25,c:6,enfant:'tab[1]'},1:{papa:'tab[0]'}}" );
var retCaseDep = parseChaine(b)
assert.equal(  retCaseDep.b, 25 );
assert.equal(  retCaseDep.enfant.papa, retCaseDep );

https://github.com/bormat/serializeStringifyParseCyclicObject

Edit: I have transform my script for NPM https://github.com/bormat/borto_circular_serialize and I have change function names from french to english.

Answer

Assuming you do want to keep the cyclic references (i.e. encode a cyclic data structure with a non-cyclic one), which is of course more work than to just delete or ignore them:

Douglas Crockford's answer: cylce.js

My improvement (of performance) of that method: my answer to related SO question

Answer

This is kind of an alternate-answer, but since what a lot of people will come here for is debugging their circular objects and there's not really a great way to do that without pulling in a bunch of code, here goes.

One feature that's not as well-known as JSON.stringify() is console.table(). Simply call console.table(whatever);, and it will log the variable in the console in tabular format, making it rather quite easy and convenient to peruse the variable's contents.

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