[Knockout] conditionally add attribute

data-bind="
    attr:{
     'selected': typeof(selected) !== 'undefined' ? 'selected' : null  

       }
"

Source : http://stackoverflow.com/questions/12963023/conditionally-add-an-element-attribute-in-knockout-js

[Knockout] Elements are showing up too early, and go away after the corresponding bind variable is initialized

<div style="display: none" data-bind="visible: true">
...
</div>

The visible binding would come through when bound and clear the display style.


Source : https://groups.google.com/forum/#!topic/knockoutjs/_oCWFJUBaq4

[Knockout] How to define which properties are serialized in JSON ?

//we have a person structure, with a first name, a last name, 
//and a full name (computed field) :
function Person(first, last) {    
    this.first = ko.observable(first);    
    this.last = ko.observable(last);    
    this.full = ko.computed(function() {
        return this.first() + " " + this.last();
    }, this);
}

• Solution 1

//we define which properties are serialized in JSON 
//(in this case, only full) and how they are serialized 
//(in this case, a simple string) :
Person.prototype.toJSON = function() {
   //only full :
   return ko.utils.unwrapObservable(this.full); // we return a string of the value
};
var person=new Person("a","b");
console.log(ko.toJSON(person)); 
// => it will generate : "a b"

• Solution 2

//we define which properties are serialized in JSON 
//(in this case, first + last name):
Person.prototype.toJSON = function() {
    var copy = ko.toJS(this); //easy way to get a clean copy
    delete copy.full; //remove an extra property
    return copy; //return the copy to be serialized
};
var person=new Person("a","b");
console.log(ko.toJSON(person)); 
// => it will generate : {"first":"a", "last":"b"}

Source :http://www.knockmeout.net/2011/04/controlling-how-object-is-converted-to.html