Detecting change to Knockout view model

Question

Sure this is a very easy question to answer but is there an easy way to determine if any property of a knockout view model has changed?

Answer 1

You can subscribe to the properties that you want to monitor:

myViewModel.personName.subscribe(function(newValue) {
    alert("The person's new name is " + newValue); 
});

This will alert when personName changes.

Ok, so you want to know when anything changes in your model...

var viewModel = … // define your viewModel

var changeLog = new Array();  

function catchChanges(property, value){
    changeLog.push({property: property, value: value});
    viewModel.isDirty = true;
}

function initialiseViewModel()
{
    // loop through all the properties in the model
    for (var property in viewModel) {

        if (viewModel.hasOwnProperty(property)) { 

            // if they're observable
            if(viewModel[property].subscribe){

                // subscribe to changes
                viewModel[property].subscribe(function(value) {
                    catchChanges(property, value);
                });
            }
        }
    }
    viewModel.isDirty = false;
}

function resetViewModel() {
    changeLog = new Array();  
    viewModel.isDirty = false;
}

(haven't tested it - but you should get the idea)