Function that replace circular js object dependency with "[Circular]" so it can be consumed by JSON.stringify

fixCircular.js

// DISCLAIMER
// Original function was updated to a faster and es5-supporting version by @Quacky2200

var replaceCircular = function(val, cache) {

    cache = cache || new WeakSet();

    if (val && typeof(val) == 'object') {
        if (cache.has(val)) return '[Circular]';

        cache.add(val);

        var obj = (Array.isArray(val) ? [] : {});
        for(var idx in val) {
            obj[idx] = replaceCircular(val[idx], cache);
        }

        cache.delete(val);
        return obj;
    }

    return val;
};

// var a = { f: "asd", b: undefined }
// var b = { h: 123, a: a }
// a.b = b
// console.log(JSON.stringify(replaceCircular(a)))
// { "f": "asd", "b": { "h": 123, "a": "[Circular]" } }

Wow, you people are great! @Quacky2200 I'll update the original to replaceCircular6 and mention you if you don't mind