Setting value of Observable not updating in Knockout

Question

(There are a ton of questions every day that link back to why can't I set the value of my observable, instead of having so many different answers saying the same thing I wanted to create a question to refer back to for everyone)

Setting value of Knockout Observable / Observable Array doesn't update

Setting the value of my observable observableArray isn't updating!

Adding an item to an Observable Array

Why can't I add an item into my Knockout observable array?

Setting value of Knockout Observable / Observable Array doesn't update

You need to use the setter function to update the value of your observable / observableArray -

Ex. 1 (observable) -

var name = 'John';
var myValue = ko.observable();
myValue(name); // Set myValue equal to John, update any subscribers

var newObservable = ko.observable('Bill');
myValue(newObservable()); // Set myValue equal to the value of newObservable, which is Bill

Ex. 2 (observableArray) -

var names = ['John', 'William', 'Dave'];
var myArray = ko.observableArray();
myArray(names); // Set myArray equal to the array of names John, update any subscribers

var newArray = ko.observableArray(['Sanford']);
myArray(newArray()); // Makes a clone of the array

Note See this Question to understand why this probably not what you are trying to do - What is the best way of cloning/copying an observablearray in knockoutJS?

Adding an item to an Observable Array

You need to push the item into the observableArray, not the underlying value of the observableArray -

var name = 'John';
var myValue = ko.observable(name);
var myArray = ko.observableArray();
myValue.push(myValue()); // Add myValue to my observableArray**

Creating a model to use/share in your view model

You can create a re-usable model to use in your view models. This is similar to using a class in C# to create objects that have common properties.

function objectModel(item) {
    var self = this;
    self.Name = ko.observable(item.name);
    self.Description = ko.observable(item.description);
}

Which can be created like -

var object = {
    name: 'John',
    description: 'a person'
}

var john = new objectModel(object);

Which could also be done by parameters instead of just objects -

function objectModel(name, description) {
    var self = this;
    self.Name = ko.observable(name);
    self.Description = ko.observable(description);
}

var john = new objectModel('John', 'a person');