Strip circular references

[zalmoxisus]

While it's great that jsan can restore circular references, in many cases we want them stripped as it will affect rendering perf and could hang object traversing.

It would be useful to have an additional parameter to use it like so:

jsan.parse(obj, null, '[CIRCULAR]');

Or if it is more performant we could strip them while stringifying. I couldn't wrap my head around it, but it seems that it would be easier to do while parsing inside retrocycle.

[kolodny]

This is already possible as follows:

var jsan = require('jsan')

var obj = {}
obj.a = 1
obj.self = obj;

var set = new WeakSet();
var stringified = jsan.stringify(obj, (key, value) => {
  if (set.has(value)) return '[CIRCULAR]';;
  if (typeof value === 'object') set.add(value);
  return value;
});

console.log(stringified)

Hmm, I can't seem to save on http://requirebin.com/ but you can just copy paste it to see for yourself

Does that solve your issue?

[zalmoxisus]

I guess we obtain almost the same as just jsan.stringify(obj) (and then parsing with JSON.parse instead of jsan.parse), I don't mind showing $jsan instead of [CIRCULAR], though it was a bit confusing.

The problem however is that in case of

var o = { t: 2 };
var obj = { e1: o, e2: o}
obj.a = 1
obj.self = obj;
console.log(customJsanStringify(obj)

we get {"e1":{"t":2},"e2":"[CIRCULAR]","a":1,"self":"[CIRCULAR]"}, but e2 is not a circular reference.

We should also account if we're including the parent, which maybe better to handle in decycle, as we have already there the structure? Or maybe when restoring the structure back from jsan.parse?

[kolodny]

Hmm, that's not a trivial problem. I guess we can detect something like that by checking that path.indexOf(foundPath) === 0 by

jsan/lib/cycle.js

Line 79 in 0867ecf

var foundPath = map.get(value);

but I'm not sold on baking that into jsan. Can you think of a less hacky implementation?

[zalmoxisus]

I'll try to convince you :-D

The idea is that most of the time people get circular references because they are including React components inside the object (accidentally or intended), and they are not interested to see the whole circular structure of that component. We have to remove them everytime we want to show the state or comparing states. Removing them outside jsan will be less performant.

If we implement it as an option, it shouldn't affect the perf of the default implementation:

      if (typeof value === 'object' && value !== null) {
+        if (options['circular'] === false && path.indexOf(foundPath) === 0) {
+          return '[CIRCULAR]';
+        }
        var foundPath = map.get(value);
        if (foundPath) {
          return {$jsan: foundPath};
        }
        map.set(value, path);
      }

Or to gain some perf from not replacing paths inside jsan.parse in this case:

      if (typeof value === 'object' && value !== null) {
+        if (options['circular'] === false) {
+          if (path.indexOf(foundPath) === 0) {
+            return '[CIRCULAR]';
+          }
+        } else {
        var foundPath = map.get(value);
        if (foundPath) {
          return {$jsan: foundPath};
        }
+      }
        map.set(value, path);
      }

Or even moving that part inside a function we can call, not to check options['circular'] === false everytime:

      function includePath() {
        if (options['circular'] === false) {
          return function() {
            if (path.indexOf(foundPath) === 0) {
              return '[CIRCULAR]';
            }
          }
        }
        return function() {
          var foundPath = map.get(value);
          if (foundPath) {
            return {$jsan: foundPath};
          }
        }
      }

Of course, there are already solutions like json-stringify-safe (maybe even more performant for this case than checking path.indexOf for every value), but we want all the goodies of jsan.

[kolodny]

Ok, I'm convinced. I've played around with it and it doesn't seem to have any perf hit I want to play around with the api some more first. I'll push a release soon 3dbebf0

[kolodny]

published to 3.1.5. Usage is undocumented but can be seen here:

https://github.com/kolodny/jsan/blob/master/test/unit.js#L77-L85

For your use case you would just pass in a string '[Circular]'

[zalmoxisus]

It works just amazing! Thanks a lot for your effort on this!