As you can see from the preceding section, this automatic conversion feature may be a problem when you want to add numbers together instead of concatenating them. JavaScript includes features that allow you to work around this issue.

Note that this is only a problem when you're using the + operator. Because JavaScript uses the same operator for two different purposes (addition and string concatenation), it's not always clear to JavaScript whether data should be considered a number or a string. If you use any other mathematical operators in a statement, JavaScript makes the appropriate conversions, as in the first example in the previous section.

You can also use any of the methods associated with JavaScript's built-in Math object to make sure JavaScript recognizes data as numeric; for example, you can use the round method to round a number to the closest integer value:

var a = "5.1";
// the value of a is the string "5.1"
var a = Math.round (a);
// the value of a is now 5, and JavaScript 
treats it as numerical data

If the decimal portion is greater than or equal to .5, it's rounded up; otherwise, it's rounded down.

You can also use the parseInt () function to convert a string to a number; for example:

var a = "5.1";
// the value of a is the string "5.1"
var a = parseInt (a);
// the value of a is now 5, and JavaScript treats 
it as numerical data

parseInt() converts a string to an integer. It can also take numbers from the beginning of a string and leave the rest; for example, parseInt ("123abc"); returns the numeric value 123.

And finally, a simple way to convert strings to numbers is to multiply them by 1; for example:

var a = 2;
// a is a number
var b = "5";
// b is a string
b = b * 1;
// b is now a number
var c = b + a;
// the value of c is now 7

Moving On

This lesson showed you how to add scripts to HTML pages. You also learned important terminology that'll come in handy in later lessons. In the Lesson 3, you'll see how automatic conversion can be important when obtaining numeric information from users. But, no problem, right? You can now apply the techniques you learned in this lesson to make sure that numbers are treated as numbers.

Before you move on to Lesson 3, don't forget to do the assignment and take the quiz. In addition, visit the Message Board to find out what your fellow students are talking about.