1.3 Changing String Case

NN 2, IE 3

1.3.1 Problem

You want to convert a string to all upper- or lowercase letters.

1.3.2 Solution

Use the two dedicated String object methods, toLowerCase( ) and toUpperCase( ), for case changes:

var myString = "New York";
var lcString = myString.toLowerCase( );
var ucString = myString.toUpperCase( );

Both methods return modified copies of the original string, leaving it intact. If you want to replace the value of a variable with a case-converted version of the original string (and thus eliminate the original string), reassign the results of the method to the same variable:

myString = myString.toLowerCase( );

Do not, however, redeclare the variable with a var keyword.

1.3.3 Discussion

Because JavaScript strings (like just about everything else in the language) are case-sensitive, it is common to use case conversion for tasks such as testing the equivalency of a string entered into a text box by a user against a known string in your code. Because the user might include a variety of case variations in the entry, you need to guard against unorthodox entries by converting the input text to all uppercase or all lowercase letters for comparison (see Recipe 1.4).

Another common need for case conversion is preparing user entries for submission to a database that prefers or requires all uppercase (or all lowercase) letters. You can accomplish this for a user either at time of entry or during batch validation prior to submission. For example, an onchange event handler in a text box can convert the text to all uppercase letters as follows:

<input type="text" name="firstName" id="firstName" size="20" maxlength="25" 
    onchange="this.value = this.value.toUpperCase( )" />

Simply reassign a converted version of the element's value to itself.

1.3.4 See Also

Recipe 1.4 for a practical example of case conversion simplifying an important string task.