<?xml version="1.0" encoding="UTF-8"?>

<CONTENT TITLE="Objects" ID="objects">

<CONTENT TITLE="What is a native object?" ID="nativeObject">

<P>

A <DFN>native object</DFN> is any object whose semantics are fully defined by

ECMA-262.

</P>

<P>

Some <DFN>native objects</DFN> are <DFN>built-in</DFN>; others, such as <DFN>user-defined</DFN> objects,

may be constructed during the execution of an ECMAScript program.

</P>

<P>

Example:

</P>

<CODE>

// Native built-in objects:

var m = Math, // Built-in Math object.

slice = Array.prototype.slice, // Built-in native method.

o = {}, // Native user-defined object.

f = function(){}, // Native user-defined function.

d = new Date(),

a = [],

e = new Error("My Message.");

</CODE>

See also:

<MOREINFO>

<URL>http://dmitrysoshnikov.com/ecmascript/chapter-7-2-oop-ecmascript-implementation/</URL>

</MOREINFO>

</CONTENT>

<CONTENT TITLE="What is a built-in object?" ID="builtInObject">

<P>

A <DFN>built-in</DFN> object is any object supplied by an ECMAScript

implementation, independent of the host environment, that is present

at the start of the execution of an ECMAScript program.

</P>

<P>

ECMA-262 3rd Edition defines the following <DFN>built-in</DFN> objects:

</P>

<LIST TYPE="DL" ID="builtInsList">

<DT>Objects</DT>

<DD><EM>global</EM>, Math</DD>

<DT>Constructors</DT>

<DD>Object, Function, Array, String, Boolean, Number, Date, RegExp</DD>

<DT>Errors</DT>

<DD>Error, Date, EvalError, RangeError, ReferenceError, SyntaxError, TypeError, URIError</DD>

<DT>Functions</DT>

<DD>eval, parseInt, parseFloat, isNaN, isFinite, decodeURI,

decodeURIComponent, encodeURI, encodeURIComponent</DD>

</LIST>

<P>

ECMA-262 Edition 5 defines also the built-in object <ICODE>JSON</ICODE>.

</P>

<P>

Nonstandard <DFN>built-in</DFN> objects may include <ICODE>RuntimeObject</ICODE>,

<ICODE>String.prototype.link</ICODE>, <ICODE>CollectGarbage</ICODE>, and more.

</P>

</CONTENT>

<CONTENT TITLE="What is a host object?" ID="hostObject" NUMID="2_8">

<P>

A <DFN>host object</DFN> is any object supplied by the host environment to

complete the execution environment of ECMAScript.

</P>

<P>

A <DFN>host object</DFN> is not part of the ECMAScript implementation, but is

exposed to the ECMAScript implementation.

</P>

<P>

A <DFN>host object</DFN> may be implemented as a native ECMAScript object, however

this is not required. For example, Internet Explorer implements many

scriptable DOM objects as ActiveX Objects, often resulting in unexpected errors.

</P>

<P>

Availability and behavior of a host object depends on the host environment.

</P>

<P>

For example, in a browser, <ICODE>XMLHttpRequest</ICODE> might be available, with or

without standard or proprietary features or events. Windows Script Host object model

has the <ICODE>WScript</ICODE> object available.

</P>

<P>

For information on a particular host object, consult the pertinent

documentation available for the implementation(s). For web browsers,

this usually includes the w3c specifications as well as documentation

for that browser.

See also:

</P>

<MOREINFO>

<URL>notes/code-guidelines/#hostObjects</URL>

<URL>http://peter.michaux.ca/articles/feature-detection-state-of-the-art-browser-scripting</URL>

</MOREINFO>

</CONTENT>

<CONTENT TITLE="When should I use eval?" ID="eval" NUMID="4_40">

<P>

The <ICODE>eval</ICODE> function should <EM>only</EM> be used when it is necessary to

evaluate a string supplied or composed at run-time; the string

can be anything from a simple (but unpredictable) expression such

as <ICODE>"12 * 2.54"</ICODE> to a substantial piece of javascript code.

</P>

<P>

When <ICODE>eval( '{"key" : 42}' )</ICODE> is called, <ICODE>{</ICODE> is interpreted as a block of

code instead of an object literal. Hence, the Grouping Operator (parentheses)

is used to force <ICODE>eval</ICODE> to interpret the JSON as an object literal:

<ICODE>eval( '({"key" : 42})' );</ICODE>.

</P>

<MOREINFO>

<URL>http://json.org/</URL>

<URL LINKTEXT="How do I access a property of an object using a string?"

>#propertyAccessAgain</URL>

<URL>notes/square-brackets/</URL>

</MOREINFO>

</CONTENT>

<CONTENT TITLE="How do I access a property of an object using a string?" ID="propertyAccessAgain" NUMID="4_39">

<P>

There are two ways to access properties: dot notation and square bracket

notation. What you are looking for is the square bracket notation in

which the dot, and the identifier to its right, are replaced with a set

of square brackets containing a string. The value of the string matches

the identifier. For example:-

</P>

<CODE>

//dot notation

var bodyElement = document.body;

//square bracket notation, using an expression

var bodyElement = document[&quot;bo&quot;+&quot;dy&quot;];

</CODE>

<MOREINFO>

<URL>notes/square-brackets/</URL>

</MOREINFO>

</CONTENT>

</CONTENT>