JavaScript: Arrays and Objects, Study notes of Computer Science

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Image you need to keep track of the scores of students in a class and you have 50 students
Declaring and handling 50 variables is not an easy task
Arrays come to the rescue
Array – Collection of values that can be treated as a unit and where you can handle each individual entry (similar to an egg carton)
You can visualize an array as a set of variables one after another
There are several ways to define arrays. var scienceScores = new Array(); // Creates an empty array var mathScores = new Array(3); // Creates an array with 3 entries var englishScores = [77, 88, 65]; // Creates an array with 3 entries // having the specified values 2 JavaScript (Arrays)
To access elements of an array  Use the [ ] operator  Integer Index values starting at zero will represent each element
Accessing array elements mathScores[0] = 70; // Assigning 70 to the first array element mathScores[1] = 80; // Assigning 80 to the second array element var total = mathScores[0] + mathScores[1]; // reading the first // and second elements 5 JavaScript (Objects)
An example of an object is the navigator object which provides information about the web browser
Among the navigator object properties you can find  appName – web browser name  appCodeName code name for the browser
You can access properties by specifying the object name, a period, and the property name or by specifying the property name using array-like syntax navigator.appName navigator[“appName”]
Notice that you can read of modify properties using the above notation
Example 3 (See Example3.html) 6 JavaScript (Frequently Used Objects)
window – Represents the window displaying the document (either the web browser window or a frame within a window). Some attributes of this object are:  closed – boolean value set to true if the window has been closed  status – text that appears in the browser’s status line
navigator – Object we described earlier
document – Refers to the document object associated with the window. This object represents the HTML document displayed in the window
location - Refers to the location object associated with the window. This object represents the URL of the document being displayed
Example 4 (See Example4.html)  This example relies on the for in construct that allow us to go through the properties for an object 7 JavaScript (Example)
By making use of functions, object properties and forms we can now define an html document with JavaScript that generates customized multiplication tables
Example 5 (See Example5.html)  Notice how we can pass properties of elements of the form to the multiplicationTable function