Kevin Smith wrote:
> For the surveyed code,
> the percentage of function expressions which do not reference "this" ranges
> between 31% and 87%. About half of all function expressions are suitable
> for conversion to BTFs. Clearly BTFs would offer immediate quantifiable
> benefit.
This is good work, but I don't think every function that doesn’t use
'this' is a supporting use case for bound-this functions, though. Many
functions are like this:
panels.each(function (p) { p.fadeIn(); });
and that function would not benefit at all from being converted to a
bound-this function.
A function is only a use case for BTF if it also *does* use the
enclosing function's 'this' somehow. That's harder to detect
statically, but even harder to find is the code that gets rewritten a
different way because of this-binding. :-\
> Of the surveyed code, about 19% of BTF candidates contain a return statement
> as their first statement. This suggests that BTF syntax should be optimized
> for both "expression functions" and multi-statement function bodies, but
> with a preference given to multi-statement functions.
This is great data to have.
Something I found really interesting about this is that if you delete
Facebook and Netflix, this number goes up to 27%. In the MooTools
code, it's 40%. So either it just varies wildly depending on
programming style, or else library code has a greater need for
"expression functions" than application code.
> Of the "expression functions", only 1.5% return an object literal. This
> suggests that BTF syntax should give preference to other forms, if there is
> a conflict.
This is good to know, too.
-j
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