Compare two objects properties in JS

Question

I need to compare two objects, and find out what properties are missing. The objects are fairly big, with several levels.

I will give short example of the type of object:

    UC = {};
    UC.start = {}
    UC.start.enableHardEccDecline = '';
    UC.start.template = {};
    UC.start.template.ecc = '';
    UC.start.template.decline = {};
    UC.start.template.decline.title = '';
    UC.start.template.decline.body = '';
    UC.general = {};...

So this is an example object. What I need to compare is just the properties. I do not care for the value. I will be comparing this object with another one very similar, but some properties might be missing.

What will you be doing with this comparison ? We can help provide a solution based on your needs, and a little more information on your end goal will help. — Christopher Messer
– Christopher Messer, Commented Sep 5, 2017 at 16:04
So one object is sent from the server, and carries several strings to be used in the html content. If some of the properties are missing, i need to stop the code, show an error page, and show all the properties that are missing — Paulo Borralho Martins
– Paulo Borralho Martins, Commented Sep 5, 2017 at 16:09

Marcin Malinowski · Accepted Answer · 2017-09-05 17:02:08Z

function compare(base, compared, deepSearch) {
  var missing = [];

  var compareProp = function (baseValue, comparedValue, path, deepSearch) {
    //console.log('comparing', path.join('.'));

    if (comparedValue === undefined) {
      console.log('missing key', path.join('.'));

        if (!deepSearch) {
          return;
        }
    }

    if (typeof baseValue === 'object') {
      Object.keys(baseValue).forEach(function (key) {
        compareProp(baseValue [key], comparedValue && comparedValue [key], path.concat(key), deepSearch);
      }); 
    }
  };

  Object.keys(base).forEach(function (key) {
    compareProp(base [key], compared [key], [key], deepSearch);
  });
}

UC = {};
UC.start = {}
UC.start.enableHardEccDecline = '';
UC.start.template = {};
UC.start.template.ecc = '';
UC.start.template.decline = {};
UC.start.template.decline.title = '';
UC.start.template.decline.body = '';
UC.general = {};

compare (UC, {}, true);

gugateider · Accepted Answer · 2017-09-05 16:28:10Z

2

I have just made a quick example here, not sure exactly how you want to apply this, but I have added the missing items to an array, which is logging it.

Obj1 should be your standard comparison object, obj2 the one received from request.

var obj1 = {};
obj1.test1 = 0;
obj1.test2 = 0;
obj1.test2222 = 0;
obj1.testLoremIpsum = 0;
obj1.lalala = 0;

var obj2 = {};
obj2.test1 = 0;
obj2.test25 = 0;
obj2.lalala1 = 0;

var k , i = 0;
var missingProps = [];

for( i in obj1 )
{
    var isFound = false;
    for( k in obj2) if( i == k ) isFound = true;
    if(!isFound) missingProps.push( i );
}
console.log(missingProps);

answered Sep 5, 2017 at 16:28

gugateider

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2 Comments

Marcin Malinowski Over a year ago

This piece of code will only go 1 level deep. Example data has more levels.

gugateider Over a year ago

True, I didn't notice. Will modify. Thanks!

MarkoCen · Accepted Answer · 2018-03-20 21:37:26Z

0

How about use JSON.stringify to convert object to string, then do the string comparison:

JSON.stringify(UC) === JSON.stringify(UCToBeCompared)

By using this method, you have to make sure the objects don't have circular reference, otherwise JSON.stringify would throw an exception

answered Mar 20, 2018 at 21:37

MarkoCen

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1 Comment

Paulo Borralho Martins Over a year ago

No that does not work, because I needed to know the properties missing.

i.terrible · Accepted Answer · 2017-09-05 16:21:50Z

-2

If your situation allows it I'd suggest using http://underscorejs.org/ library, rather than rolling your own solution (or go look at their implementation). In JS deep object comparison is sometimes not trivial. If you decide to roll your own solution, you would recursively iterate through the properties and compare them one by one (ignoring native / built-in object properties and perhaps inherited from some prototype).

I'll gladly elaborate if you'd like.

edited Sep 5, 2017 at 16:21

answered Sep 5, 2017 at 16:08

i.terrible

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Comments

hussain · Accepted Answer · 2020-04-09 09:53:49Z

-2

I have a made a example here. Hope it resolves your issue. It will compare Object KEYS only and return the object key which is not exist with compared object.

var a = Object.keys(obj1);
var b = Object.keys(obj2);

var missing= a.filter(function(v){
    return b.indexOf(v)==-1;
})

console.log(missing);

answered Apr 9, 2020 at 9:53

hussain

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