javascript - What is an ECMAScript "native object"?

Question

According to the ECMA-262 a native object

object in an ECMAScript implementation whose semantics are fully defined by this specification rather than by the host environment

A built-in object is defined as

object supplied by an ECMAScript implementation, independent of the host environment, that is present at the start of the execution of an ECMAScript program.

with a note

Standard built-in objects are defined in this specification, and an ECMAScript implementation may specify and define others. Every built-in object is a native object.

If a native object is fully defined by the ECMA-262 specification rather than the host environment and an ECMAScript implementation may specify and define new built-in objects, how is it that these new built-in object's can be native objects when they are not fully defined by the ECMA-262 specification?

What am I missing?

Answer 1

They're "native" because they come with the ECMAScript implementation. A host environment in generally an application consisting of an ECMAScript implementation and several other interfaces that work together. For instance,

• Web Browser — a host environment consisting of ECMAScript implementation, DOM interface, Rendering engine, UI, etc.
• Windows Script Host — a host environment consisting of ECMAScript implementation, VBScript implementation, etc.
• Node.js — a host environment consisting of ECMAScript implementation (V8), HTTP interfaces, etc.

"Built-in" objects are required to inherit from Object or Function, whereas host objects — objects provided by the host environment, but not necessarily present at the start of execution — are not required to but may (and sometimes do).

Examples of native objects defined by ECMA-262

• Object(), Array(), Date()
• Math, JSON, the Global object.

Examples of native, built-in objects not defined by ECMA-262

• Mozilla's numerous JavaScript extensions — such as WeakMap() or __proto__
• JScript's ActiveXObject() constructor and (undocumented) CollectGarbage() function

Examples of host objects

• DOM objects, document and window
• console