From:  Brian Slesinsky <>
Date:  03 Feb 2015 04:54:01 Hong Kong Time

Re: Source Maps, Debuggers, and Generated Code


I don't think this exists yet. Hiding helper functions and skipping them
while stepping is something GWT and Dart could use as well.

But as far as I know, nobody is working on defining an improved version of
sourcemaps and getting browsers on board.

- Brian

On Mon, Feb 2, 2015 at 11:57 AM, Ron Buckton 

> Many transpilers today (TypeScript, Traceur, 6to5, etc.) often need to
> emit generated code, that sometimes does not have a one-to-one mapping with
> the original source. One of the most notorious examples is the down-level
> transpile for ES6 generators, which often introduces multiple statements
> that correspond to a single statement or expression in the original source.
> TypeScript either elides mapping information for helper functions such as
> the __extends helper in some cases and in others maps the multiple steps to
> a single source span, such as how it handles a rest parameter. Traceur adds
> the generated code to the "sourcesContent" array in the source map.
> In addition, various debuggers with source-map support handle generated
> content differently. In the Chrome Dev Tools and in Visual Studio, any step
> in the debugger that is not mapped to a source span results in stepping
> through the generated javascript file until a mapping is encountered, while
> in the IE F12 tools the debugger makes every effort to keep the source
> content visible and highlights the last source span for each step in the
> generated output.
> Is there a standard approach to how this content should be mapped, or how
> stepping should be handled? I'm currently investigating whether it makes
> sense to propose an extension to the source map specification to classify a
> range in the generated output as "debugger hidden", so that a debugger will
> always step through any statements within this range. Alternatively, I'm
> interested in whether it would make sense for debuggers to treat generated
> lines with no mappings as "debugger hidden", as well as step through
> multiple operations if they all map to the same source location.
> Best regards,
> Ron
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