All "soft-bind" proposals I have heard have failed to get traction for
two reasons:
1. Binding |this| makes an abstraction with its own integrity.
Overriding the |this| binding only some of the time violates that
abstraction.
2. Implementations including beloved V8 and venerable SpiderMonkey would
have to recompile target soft-bound functions, or else provide an extra
parameter to replace what is for =>a lexical up-var reference. And extra
parameters and/or recompilation steps cost performance and code
complexity, always.
Whatever you think of (1) -- hey, sometimes abstractions need to be
broken (I'm not being sarcastic in general, but for => I disagree with
this aside) -- (2) is a big problem. If V8 and SpiderMonkey won't go for
"soft-bind", there's no hope.
/be
Yehuda Katz wrote:
I've been thinking a lot about the proposed arrows and its affect on
`this`.
To start, I'm a worried that `call` and `apply` don't "work" on arrow
function. This is of course the correct behavior for jQuery-like
use-cases, but the proposed semantics interfere with more intentional
uses of `call` and `apply`.
I'd like to propose the following:
* `call` and `apply` modify `this` in an arrow function
* `softCall` and `softApply` do not modify `this` in arrow functions,
but do modify `this` in regular functions
This would allow libraries like jQuery to continue providing advisory
`this` bindings without interfering with intentional modifications to
the `this` binding. (jQuery could do `softCall =
Function.prototype.softCall || Function.prototype.call` to quickly
"polyfill").
I'm not sure if this makes sense, but something about breaking `call`
and `apply` doesn't sit right with me.
Thoughs?
Yehuda Katz
(ph) 718.877.1325
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