Detecting and fixing circular references in JavaScript

Question

Given I have a circular reference in a large JavaScript object

And I try JSON.stringify(problematicObject)

And the browser throws

Answer 1

Just to throw my version into the mix... below is a remix of @dkurzaj 's code (which is itself a remix of @Aaron V 's, @user4976005 's, @Trey Mack 's and finally @Freddie Nfbnm 's [removed?] code) plus @darksinge 's WeakMap idea. So... this thread's Megamix, I guess :)

In my version, a report (rather than console.log'ed entries) is optionally returned as an array of objects. If a report is not required, testing stops on the first sighting of a circular reference (a'la @darksinge 's code).

Further, hasOwnProperty has been removed as Object.keys returns only hasOwnProperty properties (see: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys ).

function isCyclic(x, bReturnReport) {
    var a_sKeys = [],
        a_oStack = [],
        wm_oSeenObjects = new WeakMap(), //# see: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap
        oReturnVal = {
            found: false,
            report: []
        }
    ;

    //# Setup the recursive logic to locate any circular references while kicking off the initial call
    (function doIsCyclic(oTarget, sKey) {
        var a_sTargetKeys, sCurrentKey, i;

        //# If we've seen this oTarget before, flip our .found to true
        if (wm_oSeenObjects.has(oTarget)) {
            oReturnVal.found = true;

            //# If we are to bReturnReport, add the entries into our .report
            if (bReturnReport) {
                oReturnVal.report.push({
                    instance: oTarget,
                    source: a_sKeys.slice(0, a_oStack.indexOf(oTarget) + 1).join('.'),
                    duplicate: a_sKeys.join('.') + "." + sKey
                });
            }
        }
        //# Else if oTarget is an instanceof Object, determine the a_sTargetKeys and .set our oTarget into the wm_oSeenObjects
        else if (oTarget instanceof Object) {
            a_sTargetKeys = Object.keys(oTarget);
            wm_oSeenObjects.set(oTarget /*, undefined*/);

            //# If we are to bReturnReport, .push the  current level's/call's items onto our stacks
            if (bReturnReport) {
                if (sKey) { a_sKeys.push(sKey) };
                a_oStack.push(oTarget);
            }

            //# Traverse the a_sTargetKeys, pulling each into sCurrentKey as we go
            //#     NOTE: If you want all properties, even non-enumerables, see Object.getOwnPropertyNames() so there is no need to call .hasOwnProperty (per: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys)
            for (i = 0; i < a_sTargetKeys.length; i++) {
                sCurrentKey = a_sTargetKeys[i];

                //# If we've already .found a circular reference and we're not bReturnReport, fall from the loop
                if (oReturnVal.found && !bReturnReport) {
                    break;
                }
                //# Else if the sCurrentKey is an instanceof Object, recurse to test
                else if (oTarget[sCurrentKey] instanceof Object) {
                    doIsCyclic(oTarget[sCurrentKey], sCurrentKey);
                }
            }

            //# .delete our oTarget into the wm_oSeenObjects
            wm_oSeenObjects.delete(oTarget);

            //# If we are to bReturnReport, .pop the current level's/call's items off our stacks
            if (bReturnReport) {
                if (sKey) { a_sKeys.pop() };
                a_oStack.pop();
            }
        }
    }(x, '')); //# doIsCyclic

    return (bReturnReport ? oReturnVal.report : oReturnVal.found);
}