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up vote 11 down vote favorite
1

I have two JavaScript arrays orig (the original array of objects) and update (the updated orig array of objects) that have the same length and contain objects, and I want to output the differences between the each pair of objects.

Example:

var orig = [{enabled:"true", name:"Obj1", id:3},{enabled:"true", name:"Obj2", id:4}]; 

var update = [{enabled:"true", name:"Obj1", id:3}, {enabled:"true", name:"Obj2-updated", id:4}];

The output should be: name:"Obj2-updated"

I implemented something but it needs optimization...

for(var prop=0; prop<orig.length; prop++) {
  for(prop=0; prop<update.length; prop++) {
    if(orig[prop].enabled != update.enabled) { console.log(update.enabled) }
    if(orig[prop].name != update[prop].name) { console.log(update[prop].name) }
    if(orig[prop].id != update[prop].id) { console.log(update[prop].id) }
  }
}
share|improve this question
    
is the output a string, or an object? or an array with objects or strings, or? – Nina Scholz 21 hours ago
    
While I don't know your use-case it seems non-useful to me to have only a list of changed values, without knowing which key and in which object that changed value exists; are you sure you don't need more details? I'm not trying to belittle your question, but I'm trying to anticipate what your next question might be, if you're wrong about only needing the changed value(s). – David Thomas 21 hours ago
    
I just need that output to create a string text that says: "Hey, you changed Obj2 to Obj2-updated". But all I need is just to know which property was modified. – Pavel Valeriu 21 hours ago
    
@NinaScholz it doesn't matter if the output is a string or an object. – Pavel Valeriu 21 hours ago
1  
I'm voting to close this question because it's a continually moving target for those trying to answer. Before asking a question take some time to first work out what exactly you want. Check that the input you post is accurate (an Array of Objects, not simply two different Objects, to compare), and that you know what result you need, whether it's the changed-value, the changed-value and the key of that value, or the whole Object with the changed-value; ten minutes would have saved time for all. – David Thomas 19 hours ago
up vote 9 down vote accepted

You could filter the keys and get a result set with the updated keys.

var orig = [{ enabled: "true", name: "Obj1", id: 3 }, { enabled: "true", name: "Obj2", id: 4 }],
    update = [{ enabled: "true", name: "Obj1", id: 3 }, { enabled: "true", name: "Obj2-updated", id: 4 }],
    difference = [];

orig.forEach(function (a, i) {
    Object.keys(a).forEach(function (k) {
        if (a[k] !== update[i][k]) {
            difference.push({ id: update[i].id, key: k, value: update[i][k], index: i });
        }
    });
});

console.log(difference);

share|improve this answer
    
Can you please tell me if there is a way to log the modified object? In this case { enabled: "true", name: "Obj2-updated", id: 4 } – Pavel Valeriu 20 hours ago
7  
And you see, this is why I asked you, earlier, if you're sure you only needed the changed value. So far the question has changed, and the required return values have changed, from just the changed value, to the changed-value and the key for that value and now you've decided that you want the whole of the modified object to be returned. Please, take five minutes before asking a question to properly compose the question. – David Thomas 20 hours ago
1  
@PavelValeriu, if i would know, how the result should look like, i could give an answer. so what do you need? the object, or an index or the key/value pair or what? – Nina Scholz 20 hours ago
    
@NinaScholz it would be ideal for me if I can output a message like var 4 -> modified name to Obj2-updated...I assume that it is a combination between ES5 (the "classic style") and temptation – Pavel Valeriu 19 hours ago
2  
@PavelValeriu: Of course it's possible. Just look closely at what Nina's solution is doing, follow it step-by-step in the debugger, and you'll be able to work out how to do that. – T.J. Crowder 13 hours ago
up vote 5 down vote

Assuming, that the property names of both are identical and the values are just primitives (no objects, arrays etc.):

Object.keys( orig )
      .forEach( (key) => {
        if( orig[ key ] !== update[ key ] ) {
          console.log( update[key] );
        }
      });
share|improve this answer
    
Can I use orig[prop][key] ? – Pavel Valeriu 22 hours ago
    
@PavelValeriu To do what? In your example code, you assume, that both variables contain arrays, but they are objects actually. So your .length actually should not work (unless you set it somewhere explicitly) – Sirko 22 hours ago
    
It's not worth my posting a separate answer, given that it's essentially the same, but since the OP only wants to know which values are different (without reference to the keys, apparently) it's a little easier to use Object.values(), rather than accessing the values of the Object via the keys on each iteration (this does require that Object.values() is implemented in the browser though, obviously). – David Thomas 21 hours ago
    
@DavidThomas Out of curiosity: How would you match the values to each other using Object.values() without having access to the respective keys? – Sirko 21 hours ago
    
@Sirko sorry, my orig and update are arrays that contain objects, I will update my question – Pavel Valeriu 21 hours ago
up vote 2 down vote

Use Object.keys to cycle through your object. Something like:

var orig = {
  enabled: "true",
  name: "Obj1",
  id: 3
};

var update = {
  enabled: "true",
  name: "Obj1-updated",
  id: 3
};

var diff = {};

Object.keys(orig).forEach(function(key) {
  if (orig[key] != update[key]) {
    diff[key] = update[key];
  };
})

console.log(diff);

share|improve this answer
up vote 2 down vote

You can use a single loop to go through the properties of the original object and check against the updated object to find out which properties have been modified.

var orig = {
  enabled: "true",
  name: "Obj1",
  id: 3
};

var update = {
  enabled: "true",
  name: "Obj1-updated",
  id: 3
};

for (var key in orig) {
  if (orig[key] !== update[key]) {
    console.log(key + ': ' + update[key]);
  }
}

share|improve this answer

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