JavaScript—An Object Based Language - Beginning JavaScript - page 122

myShopping.reverse();
document.write(myShopping.join("<br />"));
} else {
document.write("That is not a valid input");
}
</script>
</body>
</html>
Save the example as ch5 _ example3.html . When you load this into your browser, you will be asked to
enter some input depending on whether you want the array to be ordered in forward or backward order.
If you enter 1 , the array will be displayed in forward order. If you enter -1 , the array will be displayed in
reverse order. If you enter neither of these values, you will be told that your input was invalid.
At the top of the script block, you define the array containing your shopping list. Next you define the
variable ord to be the value entered by the user in a prompt box:
var ord = prompt("Enter 1 for alphabetical order, " +
"and -1 for reverse order", 1);
This value is used in the conditions of the if statements that follow. The first if checks whether the
value of ord is 1 —that is, whether the user wants the array in alphabetical order. If so, the following
code is executed:
myShopping.sort();
document.write(myShopping.join("<br />"));
The array is sorted and then displayed to the user on separate lines using the join() method. Next, in
the else if statement, you check whether the value of ord is ‐1 —that is, whether the user wants the
array in reverse alphabetical order. If so, the following code is executed:
myShopping.sort();
myShopping.reverse();
document.write(myShopping.join("<br />"));
Here, you sort the array before reversing its order. Again the array is displayed to the user by means of
the join() method.
Finally, if ord has neither the value 1 nor the value ‐1 , you tell the user that his input was invalid:
document.write("That is not a valid input");
Finding Array elements—the indexOf() and lastIndexOf() Methods
As you can probably guess, the Array object's indexOf() and lastIndexOf() methods behave
similarly to the String object's methods—they return the index of an item's first and last occurrence
in an array. Consider the following code:
var colors = [ "red", "blue", "green", "blue" ];
alert(colors.indexOf("red"));
alert(colors.lastIndexOf("blue"));