The if and if/else Conditional Statements - Continued

Notice the addition not only of the else keyword and an additional statement, but also the use of the opening and closing curly braces - { } . The braces are used to encapsulate the true statement and the false statement, as well as divide the entire statement into its "if" and "else" sections. Notice also that the basic JavaScript syntax rules haven't been broken - a semi-colon is present after both the true statement and the false statement.

This is probably the most common of all of the many JavaScript statements. You'll use it often, so get a feel for it now. We'll examine a couple of working examples to help you get a feel for working with the if and if / else statement.

if (80<100)
   document.write("The expression has evaluated to true!!");

You can see the basic if statement used very simply here. Notice the "less-than" operator used within the conditional expression - "80<100". This if statement simply states that if 80 is less than 100, the statement is considered to be true. Since 80 is actually less than 100, the document.write statement is written to the screen. If the conditional expression were "101<100" (which is read as "if 101 is less than 100"), then nothing would be written to the screen as the conditional expression would have evaluated to false. Use the if statement if you want something to happen only if the conditional expression evaluates to true.

If you'd like an action to be taken when the conditional expression evaluates to false as well as true, use the else addition to provide an action to be taken when the conditional expression returns a false value, as shown below.

if (101<100) {
   document.write("The expression has evaluated to true!!");
   } else {
   document.write("The expression has evaluated to false!!");
} 

The above if / else statement says that if 101 is less than 100, write the first document.write statement to the screen. If 101 isn't less than 100 the second document.write statement is written to the screen. Since 101 is not less than 100, the conditional expression returns false, and the second document.write statement ("The expression has evaluated to false!!") is written to the screen.

Conditional Statemnts
The JavaScript Chronicles
The if and if/else Conditional Statements Cont. - Page 3

The JavaScript Chronicles