Using Javascript objects.

How to use Javascript objects.

  • In contrast to the primitive data types such as numbers and strings, objects have the ability to contain a collection of different data types, not only a single value.
  • An object will consist of an unordered collection of properties, each has a name and a value.
  • A property name can be a JavaScript identifier or a string, and each property value can be a primitive datatype or a reference to another object or function.

Creating Javascript objects with properties.

  • The easiest way to create an object is to specify a comma separated list of property name/value pairs, enclosed in curly brackets.
    var person1 ={"firstName":"George","lastName":"Collins" };
    var person2 ={"firstName":"Ricard","lastName":"Marvin" };
    var peoples={"company":"Google",p1:person1,p2:person2};
  • Javascript does not have any class, such as Java and C++, that are used to create objects.
  • In Javascript, new objects can be created using a constructor function type.
  • Constructor function types can be build-in objects like Object, Number, String and Date or it can be constructor function types that you creates on your own with the function statement.
  • So, to create an object with the constuctor function Object (base object for all other objects) you must use the keyword, new.
  • You can also use Object as a function which also returns an object.
  • This means we can create an object out of the constructor function, Object, in three ways:
    var myobj1={}; // is an ease way to create an empty object
    var myobj2= new Object(); // using constructor (Object) to create an object
    var myobj3= Object(); // using Object as a function to create an object

Using properties to unique objects.

  • All objects you create in Javascript inherits at least the properties from the Object object.
  • Whatever inherited property or not, all properties in an object are accessible in two ways:
    1. Using square bracket notation.
    2. Using the dot notation.
  • You are free to both read and write the value of all the properties this way, as they all are public.

    Example:
    <script type="text/javascript">
    var person1 ={"firstName":"George","lastName":"Collins" };
    var person2 ={"firstName":"Ricard","lastName":"Marvin" };
    var peoples={"company":"Google",p1:person1,p2:person2};
    // using square bracket .
    document.write("p1.lastname: "+peoples["p2"]["lastName"]+"<br>");
    // using dot notation.
    document.write("p1.firstname: "+peoples.p1.firstName+"<br>");
    // using an inherited method from the Object object
    document.write("people contains p2 is: "+peoples.hasOwnProperty("p2")+"<br>");
    document.write("people contains p2 is: "+peoples["hasOwnProperty"]("p2")+"<br>");
    </script>
  • Remember that a property value can be a function which you can execute (it is functions are values).
  • A contained object in an object can also contain an object, that contain an object and so on. This gives a chain of objects that can be accessed using the same notation as above.

    (variableName.object1.object2. ..... or variableName["object1"]["object2"][...]...)
  • At run-time you can also change the value of a property, add a new property or delete an existing property in an object.
  • To delete a property you must use the Javascript delete statement.

    Example:
    <script type="text/javascript">
      function Iam(){
        alert("I am "+person.firstName+" "+person.lastName);
      }
      var person ={"firstName":"George","lastName":"Collins",who:Iam };
      function show(personObj) {
        for (var prop in personObj){
          if (prop!="who"){
            document.write(prop+"="+personObj[prop]+"<br>");
          }else {
            personObj[prop]();
          }
        }
        document.write("<br>");
      }
      show(person);
      // add a property
      person.company="Google";
      // delete a property
      delete person.who;
      show(person);
    </script>

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