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For example:
// alert("Hello"); Single line comment
/* a = 10;
b = 20; Multi line comment
*/
Input and Output in JavaScript
JavaScript allows us to take input from the user with the help of prompt( ) method. We can use the
prompt( ) method in the following way:
var age = prompt("Enter your age: ");
When the preceding statement is executed, a prompt box will appear in the web browser asking
to input the age. By default, the input taken by the prompt( ) method is considered as a string in
JavaScript.
If you want to perform some mathematical calculations, then we need to convert the value into an
integer by using the parseInt( ) method. We can use the parseInt( ) method in the following way:
var num = parseInt(prompt("Enter first number: "));
The document.write( ) method is used to display output on the web page.
For example:
document.write("Hello from JavaScript");
The preceding statement will display the message “Hello from JavaScript” on the web page. Let us
create a web page to calculate the sum of two numbers in JavaScript.
<HTML>
<HEAD>
<TITLE> Statements in JavaScript </TITLE>
</HEAD>
<BODY>
<SCRIPT type="text/javascript">
var a = parseInt(prompt("Enter first number: "));
var b = parseInt(prompt("Enter second number: "));
var c;
c = a + b;
document.write("Sum of a and b is: ");
document.write(c);
</SCRIPT>
146 Computer Genius (V2.1)-VIII

