如何读取“本机代码”JavaScript 函数？

Question

Is there any way to see the declaration of JavaScript native code? Whenever I try to look at a native function in Chrome or Firefox, it says " native code ":

> String.fromCharCode
function fromCharCode() { [native code] }

What does this mean, and is there any tool which can help me to read actual code?

Answer 1

The reason Chrome or Firefox says that the code is native is that it really is native - the WebKit and Firefox developers have coded up that functionality in C or C++, not JavaScript. However, if you want to see the actual code, you can look at the source repositories for Chromium and Firefox .

Answer 2

Not within the JavaScript environment, but you can view the source for the open-source implementations.

Google V8: http://code.google.com/p/v8/source/browse

Mozilla SpiderMonkey: https://developer.mozilla.org/en/SpiderMonkey

Answer 3

Firefox now supports the inspection of "[native code]" objects via standard dev tools.

To see it in action:

1. update Firefox (definitely works w/ v68+, may work with older versions as well)
2. open dev tools
3. go to the Console
4. type the name of a native object, eg, "Document"
5. hit return
6. go nuts on all those little dropdown arrows

FireFox - inspect "native code" - Document object

Chrome still returns ƒ Document() { [native code] } , unfortunately.

Chrome - DON'T inspect "native code" - disappointment