recursive isEqual function causes Chrome freeze

Question

I have 2 large objects to compare. I want to know if they are equal.
JSON.stringify(obj1) == JSON.stringify(obj2) does not work, because the objects are dynamically created so the order of the attributes are random.

So I wrote a isEqual() as follows.

function isEqual(ar1, ar2) {
    if(ar1 !== ar2) {
        if(typeof ar1 !== typeof ar2) {
            return false;
        }
        if(ar1 == null) {
            if(ar2 == null) {
                return true;
            }
            return false;
        }
        if(ar2 == null) {
            if(ar1 == null) {
                return true;
            }
            return false;
        }
        if(typeof ar1 !== 'object') {
            return false;
        }
        if (ar1.length !== ar2.length) {
            return false;
        }
        for(var i in ar1) {
            if(!isEqual(ar1[i], ar2[i])) {
                return false;
            }
        }
        for(var i in ar2) {
            if(!isEqual(ar1[i], ar2[i])) {
                return false;
            }
        }
    }
    return true;
}

Now if I run isEqual(obj1, obj2) the tab in chrome freezes and I am not able to close the tab. I have to wait until chrome asks me to close non responding tabs after about 10 minutes. How to solve this?

If you have cycles in your objects, your recursive traversal can get stuck. — Pointy, Aug 28 '17 at 13:03
you might have circular references, you could use https://lodash.com/docs/4.17.4#isEqual to check for equality — marvel308, Aug 28 '17 at 13:07
"I have very big objects " How big? Pretty hard to help you out here without working code that demonstrates the issue. — epascarello, Aug 28 '17 at 13:07
@epascarello probably to handle properties that exist in one object but not the other, though I wouldn't do it that way. — Pointy, Aug 28 '17 at 13:12
Agree, Seems like a waste for OP to recheck everything again. So Object.keys() seems so much easier and if a key does not match, than it is not a match.... And use every() if it is an array. — epascarello, Aug 28 '17 at 13:17

Pytth · Accepted Answer · 2017-08-28T20:02:36.157

1

Use Lodash's isEqual to do this for you.

https://lodash.com/docs/4.17.4#isEqual

edited Aug 28 '17 at 20:02

answered Aug 28 '17 at 14:53

Pytth

4,008
24
29

volkinc · Answer 2 · 2017-08-28T15:44:39.700

I'd like to offer my solution. Please try it with your JSON objects. in order to check if objects have a different number of fields you can use

Object.keys(ar1).length !== Object.keys(ar2).length

 function isEqual(ar1, ar2) {
    if((ar1 === null) && (ar2 === null))
        return true;


    //console.info("Type: " + typeof ar1 + ":" + typeof ar2)
    if (typeof ar1 !== typeof ar2) {
        return false;
    }
    console.info("Length: " + ar1.length + ":" + ar2.length)
    if (ar1.length !== ar2.length) {
        return false;
    }

    if((typeof ar1 === 'object') && (typeof ar2 === 'object') && (Object.keys(ar1).length !== Object.keys(ar2).length))
        return false;

    if ((typeof ar1 !== 'object') && (typeof ar2 !== 'object')) {
        //console.info("Value is not equal: " + (ar1 !== ar2))
        if (ar1 !== ar2)
            return false;
        else 
            return true;
    }
    for (var i in ar1) {
        //console.info("Values:" + ar1[i] + ":" + ar2[i])
        if (!isEqual(ar1[i], ar2[i])) {
            return false;
        }
    }
    return true;
}
var obj1 = {
    a : 1,
    b :[1, 2, 3],
    c: {a:1}

};
var obj2 = {
    a : 1,
    b : [1, 2, 3],
    c: {a:1},
    d:1
};
isEqual(obj1, obj2)

I needed the second loop because sometimes there are some attributes in obj 2 which are not present in obj1. At first I had only one loop, but in some circumstances this `isEqual` considered two objects equal even if they weren't. — S.Babovic, Aug 28 '17 at 14:32
Ah. i thought .arr.length should take case about. Can you give me an example? — volkinc, Aug 28 '17 at 14:35
added check for isEqual(null,null) and null combinations that were missing — volkinc, Aug 28 '17 at 14:46

recursive isEqual function causes Chrome freeze

2 Answers2