On Tue, May 5, 2009 at 2:59 PM, Brendan Eich <bren...@mozilla.com> wrote: > On May 5, 2009, at 11:37 AM, Peter Michaux wrote: >> On Mon, May 4, 2009 at 10:26 PM, Brendan Eich <bren...@mozilla.com> wrote:
>> People often write the following at the >> beginning of functions for optional parameters >> >> optionalParam = optionalParam || defaultVal; >> >> I believe what they are really trying to write is >> >> optionalParam = optionalParam === undefined ? defaultValue : >> optionalParam; >> >> which is what ??= would do. > > You could be right, but the fact is people use ||, which equates falsy > values to not short-circuit the defaultVal evaluation. This is what the code > does, not necessarily what was meant. It might be better to pave this > cowpath and not try to sell the ?? super-highway ;-). A lot of people don't understand JavaScript falsey value equality and since || works in their server-side language they assume it works the same way in JavaScript. It compiles and runs after all! ;-) A small marketing campaign to encourage the ?: version above might change what people use. >> I think optional parameters are the nuisance use case that is fueling >> any discussion about a ||= or ??= operator. > > Nuisance to you, useful to others I think I was unclear. Optional parameters are definitely useful. It is the following idiom's verbosity that is the nuisance (to be possibly alleviated by a new operator.) optionalParam = optionalParam || defaultValue; >> (though I think they are probably worth adding.) > > Both? I don't think ||= and ??= are very difficult to define clearly. Perhaps just a line each in terms of the expanded syntax. I don't think they would add much bloat to engines. Perhaps just better to add them both and move on to discussing classes, lambdas, or processes. >> And in this syntax will default values be used if the parameter is >> falsey or only if it is undefined? > > Only if the actual parameter is absent. Well that is more useful than the ||= or ??= idioms at the top of the function body anyway. Someone passing the value "undefined" to a function causes problems for the idioms. Someone may want to still use the ||= or ??= idioms for testing properties inside an object passed to the function. I do that when the last parameter to a function is a bunch of different named optional parameters. Unfortunately simple idiom tests for properties inside an object could still be fooled if someone sets a property to "undefined". Peter _______________________________________________ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
