radio object
A set of radio buttons on an htm form. A set of radio buttons lets the user choose one item from a list.
语法
To define a set of radio buttons, use standard htm 语法 with the addition of the onClick event handler: <INPUT
TYPE="radio"
NAME="radioName"
VALUE="buttonValue"
[CHECKED]
[onClick="handlerText"]>
textToDisplay
NAME="radioName" specifies the name of the radio object. All radio buttons in a group have the same NAME attribute. You can access this value using the name property.
VALUE="buttonValue" specifies a value that is returned to the server when the radio button is selected and the form is submitted. This defaults to "on". You can access this value using the value property.
CHECKED specifies that the radio button is selected. You can access this value using the defaultChecked property.
textToDisplay specifies the label to display beside the radio button.
To use a radio button's properties and 用法: 1. radioName[index1].propertyName
2. radioName[index1].methodName(parameters)
3. formName.elements[index2].propertyName
4. formName.elements[index2].methodName(parameters)
radioName is the value of the NAME attribute of a radio object.
index1 is an integer representing a radio button in a radio object.
formName is either the value of the NAME attribute of a form object or an element in the forms array.
index2 is an integer representing a radio button on a form. The elements array contains an entry for each radio button in a radio object.
propertyName is one of the properties listed below.
methodName is one of the 用法 listed below.
Property of
描述
A radio object on a form looks as follows:
R&B
Jazz
Soul
A radio object is a form element and must be defined within a <FORM> tag.
All radio buttons in a radio button group use the same name property. To access the individual radio buttons in your code, follow the object name with an index starting from zero, one for each button the same way you would for an array such as forms: document.forms[0].radioName[0] is the first, document.forms[0].radioName[1] is the second, etc.
Properties
checked lets you programatically select a radio button
defaultChecked reflects the CHECKED attribute
length reflects the number of radio buttons in a radio object
name reflects the NAME attribute
value reflects the VALUE attribute
用法
Event handlers
例子
Example 1. The following example defines a radio button group to choose among three music catalogs. Each radio button is given the same name, NAME="musicChoice", forming a group of buttons for which only one choice can be selected. The example also defines a text field that defaults to what was chosen via the radio buttons but that allows the user to type a nonstandard catalog name as well. The onClick event handler sets the catalog name input field when the user clicks a radio button.
Soul and R&B
Jazz
Classical
Example 2. The following example contains a form with three text boxes and three radio buttons. The radio buttons let the user choose whether the text fields are converted to upper case or lower case, or not converted at all. Each text field has an onChange event handler that converts the field value depending on which radio button is checked. The radio buttons for upper case and lower case have onClick event handlers that convert all fields when the user clicks the radio button.
Radio object example
Last name:
First name:
City:
Convert values to:
Upper case
Lower case
No conversion
相关 the example for the link object.
相关
checkbox, form, and select objects
random method
Returns a pseudo-random number between zero and one. This method is available on Unix platforms only.
语法
Math.random()
Method of
例子//Displays a random number between 0 and 1
document.write("The random number is " + Math.random())
referrer property
Specifies the URL of the calling document when a user clicks a link.
语法document.referrer
Property of
描述
When a user navigates to a destination document by clicking a link object on a source document, the referrer property contains the URL of the source document. Evaluate the referrer property from the destination document.
referrer is a read-only property.
例子
In the following example, the getReferrer() function is called from the destination document. It returns the URL of the source document. function getReferrer() {
return document.referrer
}
reset object
A reset button on an htm form. A reset button resets all elements in a form to their defaults.
语法
To define a reset button, use standard htm 语法 with the addition of the onClick event handler: <INPUT
TYPE="reset"
NAME="resetName"
VALUE="buttonText"
[onClick="handlerText"]>
NAME="resetName" specifies the name of the reset object. You can access this value using the name property.
VALUE="buttonText" specifies the text to display on the button face. You can access this value using the value property.
To use a reset object's properties and 用法: 1. resetName.propertyName
2. resetName.methodName(parameters)
3. formName.elements[index].propertyName
4. formName.elements[index].methodName(parameters)
resetName is the value of the NAME attribute of a reset object.
formName is either the value of the NAME attribute of a form object or an element in the forms array.
index is an integer representing a reset object on a form.
propertyName is one of the properties listed below.
methodName is one of the 用法 listed below.
Property of
描述
A reset object on a form looks as follows:
A reset object is a form element and must be defined within a <FORM> tag.
The reset button's onClick event handler cannot prevent a form from being reset; once the button is clicked, the reset cannot be canceled.
Properties
name reflects the NAME attribute
value reflects the VALUE attribute
用法
Event handlers
例子
Example 1. The following example displays a text object with the default value "CA" and a reset button with the text "Clear Form" displayed on its face. If the user types a state abbreviation in the text object and then clicks the Clear Form button, the original value of "CA" is restored. State:
Example 2. The following example displays two text objects, a select object, and three radio buttons; all of these objects have default values. The form also has a reset button with the text "Defaults" on its face. If the user changes the value of any of the objects and then clicks the Defaults button, the original values are restored.
Reset object example
City:
State:
Blue
Yellow
Green
Red
Soul and R&B
Jazz
Classical
相关
button, form, and submit objects
round method
Returns the value of a number rounded to the nearest integer.
语法Math.round(number)
number is any numeric expression or a property of an existing object.
Method of
描述
If the fractional portion of number is .5 or greater, the argument is rounded to the next highest integer. If the fractional portion of number is less than .5, the argument is rounded to the next lowest integer.
例子//Displays the value 20
document.write("The rounded value is " + Math.round(20.49))
//Displays the value 21
document.write("<P>The rounded value is " + Math.round(20.5))
//Displays the value -20
document.write("<P>The rounded value is " + Math.round(-20.5))
//Displays the value -21
document.write("<P>The rounded value is " + Math.round(-20.51))
Last modified 01/01/1998 23:54:50