Document object, to make asynchronous calls to the web server, and to develop end-to-end web applications using software platforms such as
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The output is as follows:
The previous program would run and produce four pop-up windows, one after the other, displaying their respective values. A glaring problem here is that we are repetitively using the same numbers in multiple places. If we had to perform these arithmetic operations on a different set of numbers, we would have had to replace them at multiple locations. To avoid this situation, we would assign those numbers to temporary storage locations; these storage locations are often referred to as variables.
//This program would alert the sum of 5 and 3; alert(5+3);
/* This program would generate two alerts, the first alert would display the sum of 5 and 3, and the second alert would display the difference of 5 and 3 */ alert(5+3); alert(5-3);
Let us continue with the program:
Now let us alter the value from
6; the amount of change that we will make here is minimal. We assign the value of
6 to our variable
a, and that takes care of the rest of the process; unlike our earlier script where changes were made in multiple locations. This is shown as follows:
Code commenting is a recurring and an extremely important step in the development life cycle of any application. It has to be used to explain any assumptions and/or any dependencies that our code contains.
var and until a value is assigned to it, the value of the variable will be implicitly set to
undefined; that value is overwritten on variable initialization.
To access the value of a specific element, the reference index of that element is used. Once the reference index is identified, it can be outputted using the alert statement, as shown in the following screenshot:
Unlike variables, arrays are not typed, therefore, they can contain various types of data, as shown in the following screenshot:
To retrieve an element from a multidimensional array, we would have to use as many indexes as the levels in that array. If the multidimensional array contains an array that has the values that we want to access, we will have to choose the index where the array element exists, and then choose the index of the value inside the array that we are searching for. To retrieve the string
Three from the
multidimensionalArray example, we will have to first locate the index of the array containing the value
Three, and then find the index of the value
Three inside that array. This is shown as follows:
Objects are another way of handling data. In arrays the indexes are commonly numerical; objects give us a robust way of assigning and retrieving data. Objects are derived from the object-oriented programming concept; a programming paradigm that is very popular. Objects are a virtual representation of real-time data; they allow us to organize our data into logical groups via properties and methods. Properties describe the state of the object, while methods describe the behavior of the object. Properties are a key-value pair that holds the information. Take a look at the following:
In the previous example, we have instantiated a
person object, and then added the
lastname properties that described the object. We added behavior to the object by creating a method called
getFullName, the method accessed the object properties, retrieved the data, and alerted the output onto the screen. In this example the properties are accessed by the dot notation; we could also access a property by putting the property name in square brackets similar to an array, but it is not popular. This is shown as follows:
The second way of creating an object is by using the curly braces. Here we are introduced to the
this keyword, which provides a reference to the object's properties and methods, as shown in the following: