Check if two objects have common sub-objects

Question

I need to check if two object have common sub-objects. By common I mean that it exact same value, and not just equal values.

Something like:

function haveCommonObects(value1, value2) {
  ...
}

var common = {};
haveCommonObjects({a: common}, {b: {c: common}}) // true
haveCommonObjects({a: 1}, {b: 1}) // false

I need to check large objects, so function should be reasonable efficient. Also I can't change objects, so I can't flag sub-objects with special property. Objects create in 3rd-party library so I can't alter Object.prototype.

Ideal solution would be to get some kind of ID for every object and save it in collection that support fast lookup.

Can I make such function in JS?

so you want to compare the deepest sub object/value in each to each other? — depperm, Jun 29 '15 at 20:25
Idea behind this test is to ensure that by changing one object, I don't accidently change state of another object. — Ivan Goncharov, Jun 29 '15 at 20:30
@depperm Because I don't need to detect similar values. Instead I need to detect multiple references to the same object. — Ivan Goncharov, Jun 29 '15 at 20:32

score 1 · Accepted Answer · edited May 23 '17 at 11:43

Here's how I would do this:

function haveCommonObjects(a,b) {
    // check if a and b have any object in common, at any depth level
    if (typeof(a) !== 'object' || typeof(b) !== 'object') return false;
    for (var key in a) {
        var o = a[key];
        if (typeof(o) === 'object' && (hasObject(b,o) || haveCommonObjects(o,b)))
            return true;
    }
    return false;
}
function hasObject(x,t) {
    // check if x has a reference to object t, at any depth level
    for (var key in x) {
        var o = x[key];
        if (typeof(o) === 'object' && (o === t || hasObject(o,t)))
            return true;
    }
    return false;
}
function log(msg) { document.getElementById('log').innerHTML += msg+'<br/>'; }

var common = {};
log(haveCommonObjects({a: common}, {b: {c: common}})); // true
log(haveCommonObjects({a: 1}, {b: 1})); // false

<div id="log"></div>

Note: You should add a hasOwnProperty() filter in every for..in loop if you want to exclude inherited properties; see for..in and hasOwnProperty.

Check if two objects have common sub-objects

1 Answers1