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Select

A selection list on an HTML form. The user can choose one or more items from a selection list, depending on how the list was created.

Client-side object

Implemented in

JavaScript 1.0

JavaScript 1.1: added type property; added the ability to add and delete options.

JavaScript 1.2: added handleEvent method.

Created by

The HTML SELECT tag. For a given form, the JavaScript runtime engine creates appropriate Select objects for each selection list and puts these objects in the elements array of the corresponding Form object. You access a Select object by indexing this array. You can index the array either by number or, if supplied, by using the value of the NAME attribute.

The runtime engine also creates Option objects for each OPTION tag inside the SELECT tag.

Event handlers

Description

The following figure shows a form containing two selection lists. The user can choose one item from the list on the left and can choose multiple items from the list on the right:

A Select object is a form element and must be defined within a FORM tag.

Property Summary

Property Description
form

Specifies the form containing the selection list.

length

Reflects the number of options in the selection list.

name

Reflects the NAME attribute.

options

Reflects the OPTION tags.

selectedIndex

Reflects the index of the selected option (or the first selected option, if multiple options are selected).

type

Specifies that the object is represents a selection list and whether it can have one or more selected options.

Method Summary

Method Description
blur

Removes focus from the selection list.

focus

Gives focus to the selection list.

handleEvent

Invokes the handler for the specified event.

In addition, this object inherits the watch and unwatch methods from Object.

Examples

Example 1. The following example displays two selection lists. In the first list, the user can select only one item; in the second list, the user can select multiple items.

Choose the music type for your free CD:
<SELECT NAME="music_type_single">
   <OPTION SELECTED> R&B
   <OPTION> Jazz
   <OPTION> Blues
   <OPTION> New Age
</SELECT>
<P>Choose the music types for your free CDs:
<BR><SELECT NAME="music_type_multi" MULTIPLE>
   <OPTION SELECTED> R&B
   <OPTION> Jazz
   <OPTION> Blues
   <OPTION> New Age
</SELECT>
Example 2. The following example displays two selection lists that let the user choose a month and day. These selection lists are initialized to the current date. The user can change the month and day by using the selection lists or by choosing preset dates from radio buttons. Text fields on the form display the values of the Select object's properties and indicate the date chosen and whether it is Cinco de Mayo.

<HTML>
<HEAD>
<TITLE>Select object example</TITLE>
</HEAD>
<BODY>
<SCRIPT>
var today = new Date()
//---------------
function updatePropertyDisplay(monthObj,dayObj) {
   // Get date strings
   var monthInteger, dayInteger, monthString, dayString
   monthInteger=monthObj.selectedIndex
   dayInteger=dayObj.selectedIndex
   monthString=monthObj.options[monthInteger].text
   dayString=dayObj.options[dayInteger].text
   // Display property values
   document.selectForm.textFullDate.value=monthString + " " + dayString
   document.selectForm.textMonthLength.value=monthObj.length
   document.selectForm.textDayLength.value=dayObj.length
   document.selectForm.textMonthName.value=monthObj.name
   document.selectForm.textDayName.value=dayObj.name
   document.selectForm.textMonthIndex.value=monthObj.selectedIndex
   document.selectForm.textDayIndex.value=dayObj.selectedIndex
   // Is it Cinco de Mayo?
   if (monthObj.options[4].selected && dayObj.options[4].selected)
      document.selectForm.textCinco.value="Yes!"
   else
      document.selectForm.textCinco.value="No"
}
</SCRIPT>
<!--------------->
<FORM NAME="selectForm">
<P><B>Choose a month and day:</B>
Month: <SELECT NAME="monthSelection"
   onChange="updatePropertyDisplay(this,document.selectForm.daySelection)">
   <OPTION> January <OPTION> February <OPTION> March
   <OPTION> April <OPTION> May <OPTION> June
   <OPTION> July <OPTION> August <OPTION> September
   <OPTION> October <OPTION> November <OPTION> December
</SELECT>
Day: <SELECT NAME="daySelection"
   onChange="updatePropertyDisplay(document.selectForm.monthSelection,this)">
   <OPTION> 1 <OPTION> 2 <OPTION> 3 <OPTION> 4 <OPTION> 5
   <OPTION> 6 <OPTION> 7 <OPTION> 8 <OPTION> 9 <OPTION> 10
   <OPTION> 11 <OPTION> 12 <OPTION> 13 <OPTION> 14 <OPTION> 15
   <OPTION> 16 <OPTION> 17 <OPTION> 18 <OPTION> 19 <OPTION> 20
   <OPTION> 21 <OPTION> 22 <OPTION> 23 <OPTION> 24 <OPTION> 25
   <OPTION> 26 <OPTION> 27 <OPTION> 28 <OPTION> 29 <OPTION> 30
   <OPTION> 31
</SELECT>
<P><B>Set the date to: </B>
<INPUT TYPE="radio" NAME="dateChoice"
   onClick="
      monthSelection.selectedIndex=0;
      daySelection.selectedIndex=0;
      updatePropertyDisplay
         document.selectForm.monthSelection,document.selectForm.daySelection)">
   New Year's Day
<INPUT TYPE="radio" NAME="dateChoice"
   onClick="
      monthSelection.selectedIndex=4;
      daySelection.selectedIndex=4;
      updatePropertyDisplay
         (document.selectForm.monthSelection,document.selectForm.daySelection)">
   Cinco de Mayo
<INPUT TYPE="radio" NAME="dateChoice"
   onClick="
      monthSelection.selectedIndex=5;
      daySelection.selectedIndex=20;
      updatePropertyDisplay
         (document.selectForm.monthSelection,document.selectForm.daySelection)">
   Summer Solstice
<P><B>Property values:</B>
<BR>Date chosen: <INPUT TYPE="text" NAME="textFullDate" VALUE="" SIZE=20">
<BR>monthSelection.length<INPUT TYPE="text" NAME="textMonthLength" VALUE="" SIZE=20">
<BR>daySelection.length<INPUT TYPE="text" NAME="textDayLength" VALUE="" SIZE=20">
<BR>monthSelection.name<INPUT TYPE="text" NAME="textMonthName" VALUE="" SIZE=20">
<BR>daySelection.name<INPUT TYPE="text" NAME="textDayName" VALUE="" SIZE=20">
<BR>monthSelection.selectedIndex
   <INPUT TYPE="text" NAME="textMonthIndex" VALUE="" SIZE=20">
<BR>daySelection.selectedIndex<INPUT TYPE="text" NAME="textDayIndex" VALUE="" SIZE=20">
<BR>Is it Cinco de Mayo? <INPUT TYPE="text" NAME="textCinco" VALUE="" SIZE=20">
<SCRIPT>
document.selectForm.monthSelection.selectedIndex=today.getMonth()
document.selectForm.daySelection.selectedIndex=today.getDate()-1
updatePropertyDisplay(document.selectForm.monthSelection,document.selectForm.daySelection)
</SCRIPT>
</FORM>
</BODY>
</HTML>
Example 3. Add an option with the Option constructor. The following example creates two Select objects, one with and one without the MULTIPLE attribute. No options are initially defined for either object. When the user clicks a button associated with the Select object, the populate function creates four options for the Select object and selects the first option.

<SCRIPT>
function populate(inForm) {
   colorArray = new Array("Red", "Blue", "Yellow", "Green")
   var option0 = new Option("Red", "color_red")
   var option1 = new Option("Blue", "color_blue")
   var option2 = new Option("Yellow", "color_yellow")
   var option3 = new Option("Green", "color_green")
   for (var i=0; i < 4; i++) {
      eval("inForm.selectTest.options[i]=option" + i)
      if (i==0) {
         inForm.selectTest.options[i].selected=true
      }
   }
   history.go(0)
}
</SCRIPT>

<H3>Select Option() constructor</H3>
<FORM>
<SELECT NAME="selectTest"></SELECT><P>
<INPUT TYPE="button" VALUE="Populate Select List" onClick="populate(this.form)">
<P>
</FORM>
<HR>
<H3>Select-Multiple Option() constructor</H3>
<FORM>
<SELECT NAME="selectTest" multiple></SELECT><P>
<INPUT TYPE="button" VALUE="Populate Select List" onClick="populate(this.form)">
</FORM>
Example 4. Delete an option. The following function removes an option from a Select object.

function deleteAnItem(theList,itemNo) {
   theList.options[itemNo]=null
   history.go(0)
}

See also

Form, Radio


blur

Removes focus from the selection list.

Method of

Select

Implemented in

JavaScript 1.0

Syntax

blur()

Parameters

None

See also

Select.focus


focus

Navigates to the selection list and gives it focus.

Method of

Select

Implemented in

JavaScript 1.0

Syntax

focus()

Parameters

None

Description

Use the focus method to navigate to a selection list and give it focus. The user can then make selections from the list.

See also

Select.blur


form

An object reference specifying the form containing the selection list.

Property of

Select

Read-only

Implemented in

JavaScript 1.0

Description

Each form element has a form property that is a reference to the element's parent form. This property is especially useful in event handlers, where you might need to refer to another element on the current form.

See also

Form


handleEvent

Invokes the handler for the specified event.

Method of

Select

Implemented in

JavaScript 1.2

Syntax

handleEvent(event)

Parameters

event

The name of an event for which the object has an event handler.


length

The number of options in the selection list.

Property of

Select

Read-only

Implemented in

JavaScript 1.0


name

A string specifying the name of the selection list.

Property of

Select

Implemented in

JavaScript 1.0

Security

JavaScript 1.1: This property is tainted by default. For information on data tainting, see the Client-Side JavaScript Guide.

Description

The name property initially reflects the value of the NAME attribute. Changing the name property overrides this setting. The name property is not displayed on the screen; it is used to refer to the list programmatically.

If multiple objects on the same form have the same NAME attribute, an array of the given name is created automatically. Each element in the array represents an individual Form object. Elements are indexed in source order starting at 0. For example, if two Text elements and a Select element on the same form have their NAME attribute set to "myField", an array with the elements myField[0], myField[1], and myField[2] is created. You need to be aware of this situation in your code and know whether myField refers to a single element or to an array of elements.

Examples

In the following example, the valueGetter function uses a for loop to iterate over the array of elements on the valueTest form. The msgWindow window displays the names of all the elements on the form:

newWindow=window.open("http://home.netscape.com")
function valueGetter() {
   var msgWindow=window.open("")
   for (var i = 0; i < newWindow.document.valueTest.elements.length; i++) {
      msgWindow.document.write(newWindow.document.valueTest.elements[i].name + "<BR>")
   }
}

options

An array corresponding to options in a Select object in source order.

Property of

Select

Read-only

Implemented in

JavaScript 1.0

Description

You can refer to the options of a Select object by using the options array. This array contains an entry for each option in a Select object (OPTION tag) in source order. For example, if a Select object named musicStyle contains three options, you can access these options as musicStyle.options[0], musicStyle.options[1], and musicStyle.options[2].

To obtain the number of options in the selection list, you can use either Select.length or the length property of the options array. For example, you can get the number of options in the musicStyle selection list with either of these expressions:

musicStyle.length
musicStyle.options.length
You can add or remove options from a selection list using this array. To add or replace an option to an existing Select object, you assign a new Option object to a place in the array. For example, to create a new Option object called jeans and add it to the end of the selection list named myList, you could use the following code:

jeans = new Option("Blue Jeans", "jeans", false, false);
myList.options[myList.length] = jeans;
To delete an option from a Select object, you set the appropriate index of the options array to null. Removing an option compresses the options array. For example, assume that myList has 5 elements in it, the value of the fourth element is "foo", and you execute this statement:

myList.options[1] = null
Now, myList has 4 elements in it and the value of the third element is "foo".

After you delete an option, you must refresh the document by using history.go(0). This statement must be last. When the document reloads, variables are lost if not saved in cookies or form element values.

You can determine which option in a selection list is currently selected by using either the selectedIndex property of the options array or of the Select object itself. That is, the following expressions return the same value:

musicStyle.selectedIndex
musicStyle.options.selectedIndex
For more information about this property, see Select.selectedIndex.

For Select objects that can have multiple selections (that is, the SELECT tag has the MULTIPLE attribute), the selectedIndex property is not very useful. In this case, it returns the index of the first selection. To find all the selected options, you have to loop and test each option individually. For example, to print a list of all selected options in a selection list named mySelect, you could use code such as this:

document.write("You've selected the following options:\n")
for (var i = 0; i < mySelect.options.length; i++) {
   if (mySelect.options[i].selected)
      document.write(" mySelect.options[i].text\n")
}
In general, to work with individual options in a selection list, you work with the appropriate Option object.


selectedIndex

An integer specifying the index of the selected option in a Select object.

Property of

Select

Implemented in

JavaScript 1.0

Security

JavaScript 1.1: This property is tainted by default. For information on data tainting, see the Client-Side JavaScript Guide.

Description

Options in a Select object are indexed in the order in which they are defined, starting with an index of 0. You can set the selectedIndex property at any time. The display of the Select object updates immediately when you set the selectedIndex property.

If no option is selected, selectedIndex has a value of -1.

In general, the selectedIndex property is more useful for Select objects that are created without the MULTIPLE attribute. If you evaluate selectedIndex when multiple options are selected, the selectedIndex property specifies the index of the first option only. Setting selectedIndex clears any other options that are selected in the Select object.

The Option.selected property is more useful in conjunction with Select objects that are created with the MULTIPLE attribute. With the Option.selected property, you can evaluate every option in the options array to determine multiple selections, and you can select individual options without clearing the selection of other options.

Examples

In the following example, the getSelectedIndex function returns the selected index in the musicType Select object:

function getSelectedIndex() {
   return document.musicForm.musicType.selectedIndex
}
The previous example assumes that the Select object is similar to the following:

<SELECT NAME="musicType"> 
   <OPTION SELECTED> R&B
   <OPTION> Jazz
   <OPTION> Blues
   <OPTION> New Age
</SELECT>

See also

Option.defaultSelected, Option.selected


type

For all Select objects created with the MULTIPLE keyword, the value of the type property is "select-multiple". For Select objects created without this keyword, the value of the type property is "select-one". This property specifies the form element's type.

Property of

Select

Read-only

Implemented in

JavaScript 1.1

Examples

The following example writes the value of the type property for every element on a form.

for (var i = 0; i < document.form1.elements.length; i++) {
   document.writeln("<BR>type is " + document.form1.elements[i].type)
}

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Last Updated: 11/16/98 12:57:15

Copyright (c) 1998 Netscape Communications Corporation