Hello everyone, today we are going to make an introduction to the programming language of the Web, JavaScript.
JavaScript is a dynamic, lightweight, powerful, high-level, and an object-oriented programming language which offers great flexibility in our web designs.
In order to write a JavaScript code, we do not need a development environment. Basically, writing the commands into a text file, saving it as a HTML file and opening it with a Web Browser would be sufficient to work on JavaScript. In this tutorial, we will be placing our JavaScript code into the body section of the following HTML file;
<html>
<head>
</head>
<body>
<script language="javascript" type="text/javascript">
<!-- JavaScript Code will be written here
-->
</script>
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</body>
</html>
Let's start with some basic features of JavaScript. JS supports variables just like the other programming languages; however instead of defining the type of a variable in JS, we use var command to define a variable regardless of its type (int, string, etc.).
The following command line defines two different variables and prints them;
var num = 4;
var str = "I am a string!";
document.write("The string is: " + str,"<br/>");
document.write("The number is: " + num,"<br/>");
Output:
However, since the data type is unknown, depending on the mathematical operation (summation, multiplication, etc. ) JS acts different than most of the programming languages. The following example defines 4 different variables and some mathematical operations done with them;
var num = 5;
var num2 = 9;
var str = "3";
var str2 = "16";
document.write("Summation: " + num + str,"<br/>");
document.write("Multiplication: " + num * str,"<br/>");
// Correct Summation and Multiplication
document.write("Correct Summation: " + Number(num + Number(str)),"<br/>");
document.write("Multiplication: " + num * Number(str),"<br/>");
// Concatenation Operation = 9 + "16" = 916
document.write("Concatenation: " + String(num2) + str2,"<br/>");
Output:
Fist of all, the reason that the first summation fails is because if we are doing a summation with a string and an integer, JS converts the integer to a string and concatenates them. On the other hand, when we are doing a multiplication, the string is converted to an integer and therefore both Multiplication operations gave the same results in the example above. In order to perform correct summation and concatenation Number( ) and String( ) functions should be used.
Now let's further look into some other useful functions of JS such as toFixed( ), parseInt( ) and typeof( ).
var num3 = 3.98478532;
document.write("toFixed Output: " + num3.toFixed(4),"<br/>");
document.write("ParseInt Output: " + parseInt(num3),"<br/>");
document.write("typeof Output: " + typeof(num3),"<br/>");
- toFixed(N) function is used with float type variables and used to limit the decimal part to N digits.
- parseInt(float) function is used with float type variables and used to convert them into integers by removing the decimal part.
- typeof(type) function is used with any type of variable and used to print their data types.
document.write("Is 10 > 4 AND 6 < 9 : " + Boolean(10 > 4 && 6 < 9),"<br/>");
document.write("Is 10 == 4 OR 4 != 4 : " + Boolean(10 == 4 || 4 != 4),"<br/>");
Output:
- == checks the two values and returns true if they are the same.
- != checks the two values and returns true if they are not the same.
- a < b checks the two values and returns true if b is greater than a.
- a > b checks the two values and returns true if a is greater than b.
- && is used to check more than one conditions and returns true if all of them are correct.
- || is used to check more than one conditions and returns true if any of them is correct.
Keywords: Tutorials, JavaScript, Programming, Introduction
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