blocks|key|301463|text|这取决于实现；the+specification是对语言及其工作原理的完整描述，实现可以自由地以任何他们喜欢的方式满足实现。一些实现(从外部看)似乎纯粹是一个旧意义上的解释器；其他的可能编译成字节码，也可能不编译成字节码；V8+(+Chrome、Chromium、Brave、Node.js和其他浏览器中的JavaScript引擎)过去编译成机器码(twice，用于应用程序中的热点)，但现在开始解析字节码并在解释器中运行它，并且只在必要时编译热点(details)。(还有一种V8模式，它只进行解释，他们正在为不能在运行时编译的环境进行试验，比如iOS，在这种环境中，非苹果应用程序不允许分配可执行内存。)|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|301464|V8团队(V8是Chromium和Chrome中的JavaScript引擎)定期发布描述，描述他们是如何从V8中获得惊人的速度的。你可以在V8+blog上找到其中的一些。|301465|当然，您也可以绕过任何开源实现的代码。据我所知，V8和SpiderMonkey+(Mozilla的引擎)是两个主要的开源软件。|301466|entityMap|0|LINK|mutability|MUTABLE|url|https://tc39.es/ecma262/|1|http://blog.chromium.org/2010/12/new-crankshaft-for-v8.html|2|https://v8.dev/blog/launching-ignition-and-turbofan|3|https://v8.dev/blog^0|7|H|0|4V|5|1|69|7|2|0|1X|7|3|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@$A|W|B|X|1|Y]|$A|Z|B|10|1|11]|$A|12|B|13|1|14]]|C|$]]|$1|D|3|E|5|6|7|15|8|@]|9|@$A|16|B|17|1|18]]|C|$]]|$1|F|3|G|5|6|7|19|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|1A|8|@]|9|@]|C|$]]]|I|$J|$5|K|L|M|C|$N|O]]|P|$5|K|L|M|C|$N|Q]]|R|$5|K|L|M|C|$N|S]]|T|$5|K|L|M|C|$N|U]]]]

It's up to the implementation; <a href="https://tc39.es/ecma262/" rel="noreferrer">the specification</a> is the full description of the language and how it's supposed to work, implementations are free to satisfy that implementation in any way they like. Some implementations seem (from the outside) to run it purely as an interpreter in the old sense; others may or may not compile to bytecode; V8 (the JavaScript engine in Chrome, Chromium, Brave, Node.js, and others) used to compile to machine code (<a href="http://blog.chromium.org/2010/12/new-crankshaft-for-v8.html" rel="noreferrer">twice</a>, for hotspots in the app), but now starts out parsing to bytecode and running it in an interpreter and only compiling hotspots as necessary (<a href="https://v8.dev/blog/launching-ignition-and-turbofan" rel="noreferrer">details</a>). (There's also a V8 mode where it only interprets, which they're experimenting with for environments where compiling at runtime isn't an option, such as iOS where non-Apple apps aren't allowed to allocate executable memory.)

The V8 team (V8 being the JavaScript engine in Chromium and Chrome) periodically publish descriptions of how they get the fantastic speed out of V8 that they do. You may find some of that on the <a href="https://v8.dev/blog" rel="noreferrer">V8 blog</a>.

Naturally, you can also kick around the code of any of the open-source implementations. V8 and SpiderMonkey (Mozilla's engine) are the two major open-source ones I know.

blocks|key|4177751|text|这可能会有所帮助：http://www.ecma-international.org/publications/standards/Ecma-262.htm|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4177752|没有关于如何转换为字节码的规范(这取决于浏览器开发人员)，但是有关于语言应该如何行为的规范|4177753|entityMap|0|LINK|mutability|MUTABLE|url|http://www.ecma-international.org/publications/standards/Ecma-262.htm^0|9|1X|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

This may help : <a href="http://www.ecma-international.org/publications/standards/Ecma-262.htm" rel="nofollow">http://www.ecma-international.org/publications/standards/Ecma-262.htm</a>

There is no spec for how to translate into bytecode (That is up to the browser developers) but there are specs about how the language should behave

blocks|key|1317823|text|对于Firefox，它的字节码有一些规范：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1317824|https://developer.mozilla.org/en-US/docs/Mozilla/Projects/SpiderMonkey/Bytecodes+https://developer.mozilla.org/en-US/docs/Mozilla/Projects/SpiderMonkey/Internals/Bytecode|offset|length|1317825|对于V8，它被直接编译成本机代码：|1317826|http://jayconrod.com/posts/51/a-tour-of-v8-full-compiler|1317827|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Mozilla/Projects/SpiderMonkey/Bytecodes|1|https://developer.mozilla.org/en-US/docs/Mozilla/Projects/SpiderMonkey/Internals/Bytecode|2^0|0|0|28|0|29|2H|1|0|0|0|1K|2|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@$D|W|E|X|1|Y]|$D|Z|E|10|1|11]]|A|$]]|$1|F|3|G|5|6|7|12|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|13|8|@]|9|@$D|14|E|15|1|16]]|A|$]]|$1|J|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|K|$L|$5|M|N|O|A|$P|Q]]|R|$5|M|N|O|A|$P|S]]|T|$5|M|N|O|A|$P|I]]]]

For Firefox there's some specifications on its bytecodes:

<a href="https://developer.mozilla.org/en-US/docs/Mozilla/Projects/SpiderMonkey/Bytecodes" rel="nofollow">https://developer.mozilla.org/en-US/docs/Mozilla/Projects/SpiderMonkey/Bytecodes</a>
<a href="https://developer.mozilla.org/en-US/docs/Mozilla/Projects/SpiderMonkey/Internals/Bytecode" rel="nofollow">https://developer.mozilla.org/en-US/docs/Mozilla/Projects/SpiderMonkey/Internals/Bytecode</a>

For V8 it's compiled to native code directly:

<a href="http://jayconrod.com/posts/51/a-tour-of-v8-full-compiler" rel="nofollow">http://jayconrod.com/posts/51/a-tour-of-v8-full-compiler</a>

blocks|key|4177864|text|Javascript+(顾名思义)是一个动态的scripting+language。这意味着它的代码在运行时由web浏览器的Javascript引擎分析和执行。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4177865|这取决于Web浏览器如何处理Javascript。有些可能会生成中间语言或字节码。有些人可能会直接分析和执行它。|4177866|以下是执行Javascript+(在运行时解析和执行)的最简单方法的步骤：|4177867|4177868|解析和预处理(recursive+descent或otherwise)|unordered-list-item|4177869|Analysis|4177870|Execution|4177871|4177872|4177873|Chrome's+Javascript+Engine将Javascript编译成本机平台特定的机器码(为了优化性能)，它还具有Garbage+Collection机制。|4177874|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Scripting_language|1|http://en.wikipedia.org/wiki/Recursive_descent_parser|2|http://code.google.com/p/v8/|3|http://en.wikipedia.org/wiki/Garbage_collection_%2528computer_science%2529^0|N|I|0|0|0|0|0|7|H|1|0|0|0|0|0|0|Q|2|1R|I|3|0^^$0|@$1|2|3|4|5|6|7|17|8|@]|9|@$A|18|B|19|1|1A]]|C|$]]|$1|D|3|E|5|6|7|1B|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|1C|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|1D|8|@]|9|@]|C|$]]|$1|I|3|J|5|K|7|1E|8|@]|9|@$A|1F|B|1G|1|1H]]|C|$]]|$1|L|3|M|5|K|7|1I|8|@]|9|@]|C|$]]|$1|N|3|O|5|K|7|1J|8|@]|9|@]|C|$]]|$1|P|3|-4|5|6|7|1K|8|@]|9|@]|C|$]]|$1|Q|3|-4|5|6|7|1L|8|@]|9|@]|C|$]]|$1|R|3|S|5|6|7|1M|8|@]|9|@$A|1N|B|1O|1|1P]|$A|1Q|B|1R|1|1S]]|C|$]]|$1|T|3|-4|5|6|7|1T|8|@]|9|@]|C|$]]]|U|$V|$5|W|X|Y|C|$Z|10]]|11|$5|W|X|Y|C|$Z|12]]|13|$5|W|X|Y|C|$Z|14]]|15|$5|W|X|Y|C|$Z|16]]]]

Javascript (as it's name suggests) is a dynamic <a href="http://en.wikipedia.org/wiki/Scripting_language" rel="nofollow">scripting language</a>. Meaning that it's code is analysed and executed at runtime by the web-browser's Javascript engine. 

It is up to the Web-browser, how it wants to deal with Javascript. Some may generate an intermediate language, or bytecode. Some may directly analyse and execute it.

Here are the steps to the simplest way to execute Javascript (parsing and executing at runtime):

<li>Parsing and Preprocessing (<a href="http://en.wikipedia.org/wiki/Recursive_descent_parser" rel="nofollow">recursive descent</a> or otherwise)</li>
<li>Analysis</li>
<li>Execution

<hr>

<a href="http://code.google.com/p/v8/" rel="nofollow">Chrome's Javascript Engine</a> compiles Javascript to native platform-specific machine code (for optimum performance) It also has a <a href="http://en.wikipedia.org/wiki/Garbage_collection_%28computer_science%29" rel="nofollow">Garbage Collection</a> Mechanism.

blocks|key|4177917|text|除了已经给出的有用的、具体的答案之外，如果性能是你的主要兴趣，那么“自适应优化”这句话可能值得一查。JavaScript及其解释器只是需要在运行时将其他代码转换为机器码的系统的最新实例，因此有很多更广泛的读物。可以很容易地将Pascal、Smalltalk、Java等字节码形式视为在任意硬件上运行已定义语言的过程中的中间形式-例如，苹果的SquirrelFish+explicitly创建字节码并在其上使用即时编译器。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4177918|entityMap|0|LINK|mutability|MUTABLE|url|http://www.webkit.org/blog/214/introducing-squirrelfish-extreme/^0|53|A|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

In addition to the useful, specific answers already given, the phrase 'adaptive optimisation' is probably worth looking up if performance is your main interest. JavaScript and its interpreters are just the latest instance of systems that need to convert something else to machine code at runtime, so there's plenty of wider reading. The bytecode forms of Pascal, Smalltalk, Java, etc can easily enough be viewed as an intermediate form in the process of running a defined language on arbitrary hardware — Apple's SquirrelFish <a href="http://www.webkit.org/blog/214/introducing-squirrelfish-extreme/" rel="nofollow">explicitly</a> creates a bytecode and uses a JIT compiler on that, for example.

I can't find information on the web how W3C languages compile to machine code. I know that the gap between the web and the processor must be somehow the browser, but how does it work and what are the steps till Javascript is executed in the processor?

Links to scientific documents would be also greatly appreciated.

How is Javascript translated to bytecode?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我在网上找不到W3C语言如何编译成机器码的信息。我知道web和处理器之间的鸿沟一定是浏览器，但它是如何工作的，在处理器中执行Javascript之前有哪些步骤？链接到科学文献也将受到极大的赞赏。

问Javascript是如何翻译成字节码的？
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