Objects
JavaScript is an object-oriented language, so at its heart are a predefined set
of objects which relate to the various components of an HTML page and their relation
to each other. To view or manipulate the state of an object requires the use of properties
and methods, which are also covered in this appendix. If an object is also used as
a property of another object, that relationship is listed following the definition.
Related properties, methods, and event handlers for each object are listed following
the definition.
anchors A piece of text that can be the target of a hypertext
link. This is a read-only object which is set in HTML with <A> tags.
To determine how many anchors are included in a document, use the length property.
document.anchors.length
Unless the anchor name is an integer, the value of document.anchor[index]
will return null.
Property of document.
See link OBJECT;
see anchor METHOD.
button An object that is a form element and must be defined
within a <form> tag and can be used to perform an action.
Property of form.
See OBJECTS reset and submit;
see PROPERTIES name and value;
see click METHOD;
see onClick EVENT HANDLER.
checkbox A form element that the user sets to on
or off by clicking and that must be defined in a <form> tag.
Using the checkbox object, you can see if the box is checked and review
the name and value.
Property of form.
See radio OBJECT;
see PROPERTIES checked, defaultChecked,
name, value;
see click METHOD;
see onClick EVENT HANDLER.
Date Replaces a normal date type. Although it does not
have any properties, it is equipped with a wide range of methods. In its current
release, Date does not work with dates prior to 1/1/70. Methods for getting
and setting time and date information are divided into four classes:
set,
get, to, and parse/UTC.
Except for the date, all numerical representation of date components begin with
zero. This should not present a problem except with months, which are represented
by zero (January) through 11 (December).
The standard date syntax is "Thu, 11 Jan 1996 06:20:00 GMT".
US time zone abbreviations are also understood; but for universal use, specify the
time zone offset. For example, "Thu, 11 Jan 1996 06:20:00 GMT+0530"
is a place five hours and 30 minutes west of the Greenwich meridian.
See METHODS getDate, getDay, getHours,
getMinutes, getMonth, getSeconds, getTime,
getTimezoneOffset, getYear, parse, setDate,
setHours, setMinutes, setMonth, setSeconds,
setTime, setYear, toGMTString,
toLocaleString,
toString.
document An object created by Navigator when a page is
loaded, containing information on the current document, such as title, background
color, and forms. These properties are defined within <body> tags.
It also provides methods for displaying HTML text to the user. You can reference
the anchors, forms, and links of a document by using the anchors, forms,
and links arrays of the document object. These arrays contain an
entry for each anchor, form, or link in a document.
Property of window.
See frame OBJECT; see PROPERTIES alinkColor,
anchors, bgColor, cookie, fgColor,
forms,
lastModified, linkColor, links,
location, referrer,
title, vlinkColor;
see METHODS clear, close,
open,
write, writeln;
see onLoad and onUnload
EVENT HANDLERS.
elements An array of form elements in source
order, including buttons, check boxes, radio buttons, text and text area objects.
The elements can be referred to by their index:
formName.elements[index]
Elements can also be referenced by the element name. For example, a password element
called newPassword is the second form element on an HTML page. It’s value is accessed
in three ways:
formName.elements[1].value
formName.elements["newPassword"].value
formName.newPassword.value
Values can not be set or changed using the read-only elements array.
Property of form.
See length PROPERTY.
form A property of the document object. Each
form in a document is a separate and distinct object that can be referenced using
the form object. The form object is an array created as forms are
defined through HTML tags. If the first form in a document is named orderForm,
then it could be referenced as document.orderForm or document.forms[0].
Property of document.
See hidden OBJECT;
see PROPERTIES action,
elements, encoding,
forms, method, name,
target;
see submit METHOD;
see onSubmit EVENT HANDLER.
frame A window that contains HTML subdocuments that are
independently, although not necessarily, scrollable. Frames can point to
different URLs and be targeted by other frames–all in the same window. Each frame
is a window object defined using the <frameset> tag to define
the layout that makes up the page. The page is defined from a parent HTML document.
All subdocuments are children of the parent. If a frame contains definitions
for SRC and NAME attributes, then the frame can be identified
from a sibling by using the parent object as parent.frameName or
parent.frames[index].
Property of window. See document and window OBJECTS;
see PROPERTIES defaultStatus, frames, parent, self,
status, top, window; see METHODS setTimeout and
clearTimeout.
hidden A text object suppressed from appearing on an
HTML form. Hidden objects can be used in addition to cookies to
pass name/value pairs for client/server communication. Property of form.
See PROPERTIES cookie, defaultValue, name, value.
history This object is derived from the Go menu and contains
URL link information for previously visited pages. Property of document.
See location OBJECT; see length PROPERTY; see METHODS back,
forward, go.
link A location object. In addition to providing
information about existing hypertext links, the link object can also be
used to define new links. Property of document. See anchor OBJECT;
see PROPERTIES hash, host, hostname, href, length,
pathname, port, protocol, search, target;
see link METHOD; see onClick and onMouseOver EVENT HANDLERS.
location Contains complete URL information for the current
document, while each property of location contains a different portion of
the URL. Property of document. See history OBJECT; see PROPERTIES
hash, host, hostname, href, location,
pathname, port, protocol, search, target.
Math Includes properties for mathematical constants and
methods for functions. For example, to access the value of pi in an equation, use:
Math.PI
Standard trigonometric, logarithmic, and exponential functions are also included.
All arguments in trigonometric functions use radians.
See PROPERTIES E, LN10, LN2, PI, SQRT1_2,
SQRT2; see METHODS abs, acos, asin, atan,
ceil, cos, exp, floor, log, max,
min, pow, random, round, sin, sqrt,
tan. navigator Contains information on the current
version of Navigator used by the client. See OBJECTS link and anchors;
see PROPERTIES appName, appCodeName, appVersion, userAgent.
option Objects created within HTML <form>
tags and represent option buttons. A set of option buttons enables the user to select
one item from a list. When it is created, it takes the form of document.formName.radioName[index],
where the index is a number representing each button beginning with zero. Property
of form. See OBJECTS checkbox, select; see PROPERTIES
checked, defaultChecked, index, length, name,
value; see click METHOD; see onClick EVENT HANDLER.
password Created by HTML password text fields, and are
masked when entered by the user. It must be defined with an HTML <form>
tag. Property of form. See text OBJECT; see PROPERTIES defaultValue,
name, value; see METHODS focus, blur, select.
reset Correlates with an HTML reset button, which resets
all form objects to their default values. A reset object must be created
within a <form> tag. Property of form. See OBJECTS button
and submit; see PROPERTIES name and value; see click
METHOD; see onClick EVENT HANDLER.
select A selection list or scrolling list on an HTML
form. A selection list enables the user to choose one item from a list, while a scrolling
list enables the choice of one or more items from a list. Property of form.
See radio OBJECT; see PROPERTIES length, name, options,
selectedIndex; see METHODS blur and focus; see EVENT HANDLERS
onBlur, onChange, onFocus.
For the options PROPERTY of select, see defaultSelected,
index, selected, text, value. string A
series of characters defined by double or single quotes. For example:
myDog = "Brittany Spaniel"
returns a string object called myDog with the value "Brittany
Spaniel". Quotation marks are not a part of the string’s value–they are
only used to delimit the string. The object’s value is manipulated using methods
that return a variation on the string, for example myDog.toUpperCase() returns
"BRITTANY SPANIEL". It also includes methods that return HTML
versions of the string, such as bold and italics.
See text and text area OBJECTS; see length PROPERTY;
see METHODS anchor, big, blink, bold, charAt,
fixed, fontcolor, fontsize, indexOf, italics,
lastIndexOf, link, small, strike, sub,
substring, sup, toLowerCase, toUpperCase.
submit Causes the form to be submitted to the program
specified by the action property. It is created within an HTML <form>
tag. It always loads a new page, which may be the same as the current page if an
action isn’t specified. Property of form. See OBJECTS button and
reset; see PROPERTIES name and value; see METHOD click;
see EVENT HANDLER onClick.
text A one-line input field on an HTML form that accepts
characters or numbers. Text objects can be updated by assigning new contents
to its value. Property of form. See OBJECTS password, string,
textarea; see PROPERTIES defaultValue, name, value;
see METHODS focus, blur, select; see EVENT HANDLERS onBlur,
onChange, onFocus, onSelect.
textarea Similar to a text object, with the
addition of multiple lines. A textarea object can also be updated by assigning
new contents to its value. Property of form. See OBJECTS password,
string, text; see PROPERTIES defaultValue, name,
value; see METHODS focus, blur, select; see EVENT
HANDLERS onBlur, onChange, onFocus, onSelect.
window Created by Navigator when a page is loaded containing
properties that apply to the whole window. It is the top-level object for each document,
location, and history object. Because its existence is assumed,
you do not have to reference the name of the window when referring to its objects,
properties, or methods. For example, the following two lines have the same result
(printing a message to the status line):
status("Go away from here.")
window.status("Go away from here.")
A new window is created using the open method:
aNewWindow = window.open
("URL","Window_Name",["windowFeatures"])
The variable name is used to refer to the window’s properties and methods. The
window name is used in the target argument of a form or anchor tag.
See OBJECTS document and frame; see PROPERTIES defaultStatus,
frames, parent, self, status, top, window;
see METHODS alert, close, confirm, open, prompt,
setTimeout, clearTimeout; see EVENT HANDLERS onLoad and
onUnload.
- JavaScript Terms
- JavaScript Objects
- JavaScript Properties
- JavaScript Methods
- JavaScript Event Handlers
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