On Fri, Mar 30, 2012 at 4:46 AM, Felix Böhm <[email protected]> wrote:
> How about a "loose-bound" |this|, so that the function falls back to the > bound |this| instead of the global scope when no other options are > available (or `null` or `undefined` are passed to `.apply/.bind/.call`)? > > I strongly support this proposal. Any legacy utility (3rd party or otherwise) that assumes its function arguments are dynamically bound (a reasonable assumption as of ES 5.1) will be in trouble when passed hard-bound fat arrow functions. Here's a gist illustrating a simplified version of a functional mixin process and how it would break under the current fat arrow proposal. https://gist.github.com/2266911 Yes we could use the long-form function instead, but it seems unnecessarily restrictive (not to mention confusing) that the much anticipated short-form syntax should be out-of-bounds whenever there is a remote possibility that the function may at some time need invoking with a different |this| value (and how can we even anticipate such a requirement? - especially if we are writing 3rd party libraries) And yes there is an ES 5 precedent - Function::bind also makes a hard binding, but with bind there are no surprises, it is intentional and explicit - fat arrow lexical binding OTOH will probably be an unexpected side effect for those developers whose primary goal is to save key strokes. Under Felix's proposal I'm assuming a soft-lexical binding would be overridable by call and apply (provided a valid context object is passed) or by the base reference of a method invocation. In other words if a |this| value is provided, use it, otherwise default to the lexical scope instead of the global scope. I'm betting that covers most of the current |this| headaches we are trying to solve while keeping short-form syntax in play for those of us who value/rely on dynamic binding. Angus > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > >
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