Differences among native objects, built-in objects, and host objects

1、 built-in （Build-in） Objects and primitives （Naitve） The difference between objects is ： The former is always created in the engine initialization phase , It's a subset of the latter ; The latter includes some objects that are created dynamically in the running process .

2、 The engine extension object is a small collection , Generally speaking, it is relatively certain , They also belong to the native objects of the engine （ But that does not belong to ECMA Canonical native objects ）.

3、 The host object is not the native object of the engine , Instead, the host framework registers to JavaScript Objects in the engine .

4、 Some hosts will provide their own objects ／ Constructors are also known as “ Native object ”, for example Internet Explorer 7 Just provide it XMLHttpRequest() Called native —— In contrast, it was adopted in its earlier version “new ActiveXObject(‘Microsoft.XMLHTTP’)” Objects created by such methods . In this case , Readers should note “ The native object of the host ” And “ The native object of the engine ” Differences between .

One 、 Native object

ECMA-262 Put the native object （native object） Defined as “ Independent of the host environment ECMAScript Implement the provided objects ”.

Object、Function、Array、String、Boolean、Number、Date、RegExp、Error、EvalError、RangeError、ReferenceError、SyntaxError、TypeError、URIError、ActiveXObject( Server side )、Enumerator( Collection traversal class )、RegExp（ Regular expressions ）

From this we can see that , Simply speaking , The native object is ECMA-262 Defined classes （ Reference type ）.

Two 、 Built-in objects

ECMA-262 Put built-in objects （built-in object） Defined as “ from ECMAScript Implement the provided 、 All objects independent of the host environment , stay ECMAScript Appears when the program starts executing ”. This means that developers don't have to instantiate built-in objects , It has been instantiated .

The same is “ Independent of host environment ”. By definition, it seems hard to tell “ Built-in objects ” And “ Native object ” The difference between . and ECMA-262 Only two built-in objects are defined , namely Global and Math （ They are also native objects , According to the definition , Every built-in object is a native object ）.

So it's understandable . Built in objects are a kind of native objects . And it contains two kinds of objects ,Math Objects we often use , But this Global What is the object ？

Global The object is ECMAScript The most special object in , Because it doesn't really exist ！ stay ECMAScript in , There is no independent function , All functions must be methods of an object .

Be similar to isNaN()、parseInt() and parseFloat() Such method , It's all functions , But in fact , They are all Global Object method . and Global Objects have more than that .

3、 ... and 、 Host object

What is the “ Host object ”？ ECMAScript Medium “ host ” Of course, it is the running environment of our web pages , namely “ operating system ” and “ browser ”. All non-native objects are host objects （host object）, by ECMAScript Implemented host environment provided objects .

be-all BOM and DOM Objects are all host objects . Because it's different for “ host ” The content of the environment is different . In fact, it's just ,ECMAScript Officially undefined objects belong to the host object , Because most of its undefined objects pass by themselves ECMAScript The object created by the program .TML DOM yes W3C standard （ yes HTML Short for document object model ,Document Object Model for HTML）.

HTML DOM Defined for HTML A series of standard objects , And access and processing HTML Standard approach to documentation .

adopt DOM, Access to all HTML Elements , Along with the text and attributes they contain . You can modify and delete the contents , You can also create new elements .