ES6 opt-in, reloaded

Brendan Eich brendan at
Mon Jan 16 14:47:02 PST 2012

> David Herman <mailto:dherman at>
> January 16, 2012 2:18 PM
> The goal that is missing, and what I believe is the single most 
> important part of my New Year's email, is:
> 9. Allow programmers to continue thinking of JS as a single cohesive 
> language.

Thanks, this is the transcendant usability goal in my view. ES4 suffered 
for many reasons, and seeming to create too different a language was one 
of its biggest conceptual (as in problem in the abstract, not just in 
concrete proposals) flaws. Not all of this was bad PR, either.

If we have already gone too far in terms of runtime "five fingers of 
fate" changes with completion reform, we can pare back. But I'd like to 
give c.r. a chance -- it may be non-breaking.

New compile-time reforms such as modules making free variable typos be 
early errors are a feature, and the fact that they're early errors is 
pure unadulterated win.

New early errors (provided they are not prone to false positives or 
attempts to enfoce style on which reasonable people disagree) seem all 
good. Early errors under new syntax are not a forking of the language 
from being One JavaScript.

Version opt-in goes the other way, not just as a user-facing requirement 
to use an early top level pragma, but also in terms of learning, 
thinking, and further evolving the language. This is a risk for spec 
editors and TC39 -- I believe strongly that we must not fork the spec.


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