Step-by-step JavaScript interpreter, written in JavaScript

#1

Post by bcjordan » Thu, Oct 09, 2014, 7:04 PM UTC

Step-by-step JavaScript interpreter, written in JavaScript
neil.fraser.name

Re: Step-by-step JavaScript interpreter, written in JavaScript

#2

Post by hexasquid » Thu, Oct 09, 2014, 8:38 PM UTC

This is terrific. I'd love a description of what the interpreter is actually doing at each step, perhaps optionally sent to the console. This could be a wonderful tool for teaching how JavaScript works.

Re: Step-by-step JavaScript interpreter, written in JavaScript

#3

Post by foogered » Thu, Oct 09, 2014, 9:27 PM UTC

Cool project, but the title initially lead me to believe this was a tutorial on building a JavaScript interpreter. :(

Re: Step-by-step JavaScript interpreter, written in JavaScript

#4

Post by rubyn00bie » Thu, Oct 09, 2014, 9:33 PM UTC

I think itd be cool to see the tokenization happen as you step through it. The highlighting is a great step in helping understand the process.

Re: Step-by-step JavaScript interpreter, written in JavaScript

#5

Post by peetle » Thu, Oct 09, 2014, 9:33 PM UTC

Wait a minute, how does this interpreter allow multi-threaded execution without web workers?

Re: Step-by-step JavaScript interpreter, written in JavaScript

#6

Post by rubyn00bie » Thu, Oct 09, 2014, 9:34 PM UTC

foogered wrote: post #3

Cool project, but the title initially lead me to believe this was a tutorial on building a JavaScript interpreter. :(

There's on in the project on github that looks like it's originally from Google. You can probably find docs specifically on it (and it looks like the source is well documented).

Re: Step-by-step JavaScript interpreter, written in JavaScript

#7

Post by icebraining » Thu, Oct 09, 2014, 9:54 PM UTC

peetle wrote: post #5

Wait a minute, how does this interpreter allow multi-threaded execution without web workers?

Thread switching? Multi-threaded just means it allows concurrent threads; they're not necessarily parallel: https://talks.golang.org/2012/waza.slide

Re: Step-by-step JavaScript interpreter, written in JavaScript

#8

Post by jaz303 » Thu, Oct 09, 2014, 10:51 PM UTC

peetle wrote: post #5

Wait a minute, how does this interpreter allow multi-threaded execution without web workers?

It uses a small-step interpreter [1]. Rather than capturing the interpreter's state on the native call stack, small-step interpreters explicitly model said state using stacks of objects - one per active AST node - and environments. Because they're no longer bound to the stack of the implementation language, execution may be cycled, paused and resumed at will.

[1] http://matt.might.net/articles/writing-an-interpreter-substi...

Re: Step-by-step JavaScript interpreter, written in JavaScript

#9

Post by yonran » Thu, Oct 09, 2014, 11:14 PM UTC

We finally have a substitute for eval within Chrome extensions! Also could be useful for experiments e.g. simulating synchronous APIs.

Re: Step-by-step JavaScript interpreter, written in JavaScript

#10

Post by amasad » Thu, Oct 09, 2014, 11:51 PM UTC

This is great. I also implemented a JS stepping interpreter in JS [1] but using a different approach. I let the host JS environment do parsing and evaluation. I just use generators to pause executions and then pass the code through a ES6 generator transpiler[2]. See the demo[3].

[1] http://amasad.me/2014/01/06/building-an-in-browser-javascrip... [2] https://github.com/facebook/regenerator [3] http://debugjs.com/#example