JavaScript Learning notes ———— JavaScript application environment

JavaScript's application environment is mainly the host environment (host environment) and the run-time environment composition. Where the hosting environment refers to the shell (shell) and web browser, and the runtime environment is built by the JavaScript engine.

Hosting environment

A hosting environment is a design that is designed to isolate code, language, and specific platforms. On the one hand we cannot allow the browser to have a huge operating environment (virtual machine is a platform with a particularly large runtime environment), on the other hand, the server side needs a strong environment, so JavaScript is designed to "host environment" language.

The ECMAScript specification does not provide a clear definition of the hosting environment. That is, there is no standard input (stdin) or output (stdout) to which specific object it is presented. Later, RWC in the Webapis specification first proposed a "Need a Window object" browser environment. This means that in RWC or on the browser side, the input output is provided with the Window object and the Document object in it. However, the "host environment under the RWC specification" does not equal the "host environment under the JavaScript specification"

Method	Meaning
alter (smessage)	displays a message text (string) and waits for the user to respond once. The caller ignores the return information of the response
write (Stext, ...	output a piece of text, and multiple parameters will be concatenated into a single string literal.
Writein (Stext,...)	Output a piece of text (with write), multiple parameters are concatenated into a single string literal, and a newline character is appended to the end of the text (\ n)

Note: Write () and Writein are the methods of the Document object in the browser.

Shell Program

The shell is one of the hosts.

Run-time environment

Different books have inconsistent interpretations of their definitions:

For example, in the JavaScript authoritative guide, it consists of the JavaScript kernel (CORE) and the client JavaScript two parts;

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core ECMAScript , Browser object Model (BOM) three components.

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In the initial state of the run-time environment mainly includes:

1. A convention on the host

2. An engine core

3. A set of objects and APIs

4. Some of the other specifications

Common JavaScript engines

engine	apply	language	note
spidermonkey	mozilla	c
javascriptcore	safari	c++	based on KDE published KJS, supported by Apple Inc.
rhino	java	java	mainly used in the Java platform of IBM, Sun, etc.
jscript	windows		windows environment, and IE
Narcissus		Javascript	Notes

Remarks *:brendan Eich A set of code written to verify the self-realization of the JavaScript language, called "JS implemented in JS"

This article is from the "Sun nuo" blog, please be sure to keep this source http://10479756.blog.51cto.com/10469756/1919595

JavaScript Learning notes ———— JavaScript application environment