Sams Teach Yourself JavaScript in 24 Hours

Using Multiple Conditions with switch

In the previous example, you used several if statements in a row to test for different conditions. Here is another example of this technique:

if (button=="next") window.location="next.html";
else if (button=="previous") window.location="prev.html";
else if (button=="home") window.location="home.html";
else if (button=="back") window.location="menu.html";

Although this is a compact way of doing things, this method can get messy if each if statement has its own block of code with several statements. As an alternative, JavaScript includes the switch statement, which enables you to combine several tests of the same variable or expression into a single block of statements. The following shows the same example converted to use switch:

switch(button) {
    case "next":
        window.location="next.html";
        break;
    case "previous":
        window.location="prev.html";
        break;
    case "home":
        window.location="home.html";
        break;
    case "back":
        window.location="menu.html";
        break;
    default:
        window.alert("Wrong button.");
}

The switch statement has several components:

• The initial switch statement. This statement includes the value to test (in this case, button) in parentheses.

• Braces ({ and }) enclose the contents of the switch statement, similar to a function or an if statement.

• One or more case statements. Each of these statements specifies a value to compare with the value specified in the switch statement. If the values match, the statements after the case statement are executed. Otherwise, the next case is tried.

• The break statement is used to end each case. This skips to the end of the switch. If break is not included, statements in multiple cases might be executed whether they match or not.

• Optionally, the default case can be included and followed by one or more statements that are executed if none of the other cases were matched.