javascript手冊-r

描述

A radio object on a form looks as follows: <form>

<input CHECKED name=musicChoice type=radio> R&B
<input name=musicChoice type=radio> Jazz
<input name=musicChoice type=radio> Soul </form>

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

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.

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.

相关 the example for the link object.

相关

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

Math

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

document

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=""

   VALUE="buttonText"

   [onClick="handlerText"]>

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)

Property of

描述

A reset object on a form looks as follows: <form>

<input type=reset value=Defaults> </form>

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

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.

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.

相关

round method

Returns the value of a number rounded to the nearest integer.

语法

Math.round(number)

Method of

Math

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("
The rounded value is " + Math.round(20.5))

//Displays the value -20

document.write("
The rounded value is " + Math.round(-20.5))

//Displays the value -21

document.write("
The rounded value is " + Math.round(-20.51))