Object.watch() for all browsers?

Question

Please note that Object.Watch and Object.Observe are both deprecated now (as of Jun 2018).

I was looking for an easy way to monitor an object or variable for changes, and I found Object.watch(), that's supported in Mozilla browsers, but not IE. So I started searching around to see if anyone had written some sort of equivalent.

About the only thing I've found has been a jQuery plugin, but I'm not sure if that's the best way to go. I certainly use jQuery in most of my projects, so I'm not worried about the jQuery aspect...

Anyway, the question: Can someone show me a working example of that jQuery plugin? I'm having problems making it work...

Or, does anyone know of any better alternatives that would work cross browser?

Update after answers:

Thanks everyone for the responses! I tried out the code posted here: http://webreflection.blogspot.com/2009/01/internet-explorer-object-watch.html

But I couldn't seem to make it work with IE. The code below works fine in Firefox, but does nothing in IE. In Firefox, each time watcher.status is changed, the document.write() in watcher.watch() is called and you can see the output on the page. In IE, that doesn't happen, but I can see that watcher.status is updating the value, because the last document.write() call shows the correct value (in both IE and FF). But, if the callback function isn't called, then that's kind of pointless... :)

Am I missing something?

var options = {'status': 'no status'},
watcher = createWatcher(options);

watcher.watch("status", function(prop, oldValue, newValue) {
  document.write("old: " + oldValue + ", new: " + newValue + "
");
  return newValue;
});

watcher.status = 'asdf';
watcher.status = '1234';

document.write(watcher.status + "
");

user_78436 · Answer

(Sorry for the cross-posting, but this answer I gave to a similar question works fine here)

I have created a small object.watch shim for this a while ago. It works in IE8, Safari, Chrome, Firefox, Opera, etc.

user_45433 · Answer

That plugin simply uses a timer/interval to repeatedly check for changes on an object. Maybe good enough but personally I would like more immediacy as an observer.

Here's an attempt at bringing watch/unwatch to IE: http://webreflection.blogspot.com/2009/01/internet-explorer-object-watch.html.

It does change the syntax from the Firefox way of adding observers. Instead of :

var obj = {foo:'bar'};
obj.watch('foo', fooChanged);

You do:

var obj = {foo:'bar'};
var watcher = createWatcher(obj);
watcher.watch('foo', fooChanged);

Not as sweet, but as an observer you are notified immediately.

user_1215133 · Answer

The answers to this question are a bit outdated. Object.watch and Object.observe are both deprecated and should not be used.

Today, you can now use the Proxy object to monitor (and intercept) changes made to an object. Here's a basic example:

var targetObj = {};
var targetProxy = new Proxy(targetObj, {
  set: function (target, key, value) {
      console.log(`${key} set to ${value}`);
      target[key] = value;
  }
});

targetProxy.hello_world = "test"; // console: 'hello_world set to test'

If you need to observe changes made to a nested object, then you need to use a specialized library. I published Observable Slim and it works like this:

var test = {testing:{}};
var p = ObservableSlim.create(test, true, function(changes) {
    console.log(JSON.stringify(changes));
});

p.testing.blah = 42; // console:  [{"type":"add","target":{"blah":42},"property":"blah","newValue":42,"currentPath":"testing.blah",jsonPointer:"/testing/blah","proxy":{"blah":42}}]

user_3599013 · Answer

I have used Watch.js in one of my projects. And it is working fine.One of the main advantage of using this library is :

"With Watch.JS you will not have to change the way you develop."

The example is given below

//defining our object however we like
var ex1 = {
 attr1: "initial value of attr1",
 attr2: "initial value of attr2"
};

//defining a 'watcher' for an attribute
watch(ex1, "attr1", function(){
 alert("attr1 changed!");
});

//when changing the attribute its watcher will be invoked
ex1.attr1 = "other value";

This is as simple as this!

user_7236583 · Answer

This works for me

 $('#img').hide().attr('src', "path/newImage.jpg").fadeIn('slow');

Object.watch() for all browsers?

9 Answers