JavaScript Events (Cont.)
onFocus, onBlur, and onChange
The onFocus, onBlur, and onChange events are often used in combination with validation of form fields.
Below is an example of how to use the onChange event, which executes JavaScript code when a change event occurs; that is, when a select, text, or textarea field loses focus and its value has been modified.
The
lowerCase() function will be called whenever the user changes the content of the field.
The function converts the uppercase letters in the Unix shell command to lowercase letters before the command is executed:
- The keyword
this refers to the current object.
In general, in a method this refers to the calling object.
- The method
getElementById() of the object document returns the element with the specified ID.
- The method
toLowerCase() of the object string returns the calling string value converted to lowercase.
Demonstration
The following demonstration shows how the script of HTML and JavaScript is displayed on the Web.