Question

I took a small code from backbone home site, and consoled the function, in this example, sidebar.on(‘change:color’), takes the function. but it requires two parameter, one is abiously we need that is ‘color’, and we defining the element inside the function, still why we giving another parameter as ‘model’ here, what that parameter does?

if i remove that parameter send only the color, the function doesn’t work at all… any one help me to understand this?

sample function here:

var Sidebar = Backbone.Model.extend({
    promptColor : function(){
    var cssColor = prompt('Please enter a css color');
        this.set({color:cssColor});       
    }
});

window.sidebar = new Sidebar;

sidebar.on('change:color',function(model,color){ // what model parameter do here?
    console.log(model);
    $('#sidebar').css({
        background:color
    })
})

sidebar.set({color:'green'});
sidebar.promptColor();

when i console the model i got this:

d
_callbacks: Object
_changing: false
_escapedAttributes: Object
_pending: Object
_previousAttributes: Object
_silent: Object
attributes: Object
changed: Object
cid: "c1"
__proto__: x

Answer 1

It is possible that you want to know which model was affected.

Consider a case where you are listening to an event on a collection instead. Which model’s color value was modified? The model parameter tells you this.

Also, consider a case where the same handler is listening to “change:color” on multiple models. Again, you might want to know which model sent the event.

Just like in other event-driven environments, the “sender” is always passed along with the event data. model, in this case, is the sender.