On Fri, May 31, 2013 at 7:33 AM, Till Schneidereit <[email protected]>wrote:
> I couldn't find any precise definition for the spec term "present", so > this is not entirely clear to me. > > Example: > In step 7 of 15.4.3.21 Array.prototype.reduce, a TypeError must be thrown > if the optional argument `initialValue` isn't present. If a value of > `undefined` does *not* cause the argument to be present, that function can > be implemented with the following signature: > > `function ArrayReduce(callbackfn, initialValue = undefined)` > `undefined` is a valid initial value for Array.prototype.reduce. `undefined` will also trigger the default parameter, so this works until nothing is provided, which breaks Step 10. > > If, however, the value `undefined` means that the argument is present, the > signature should probably be: > > `function ArrayReduce(callbackfn, ...rest)` > With minor changes to steps 9 and 10, plus the addition of steps to check rest.length and then Get(rest, "0"), this would work. I suspect that Allen would prefer to craft some sort of spec mechanism, from this use case, for "is foo present" assertions throughout the spec. Rick > > > The question isn't entirely academic, as I'm trying to get the self-hosted > implementations of builtins in SpiderMonkey to be as close to the spec as > possible. > > > thanks, > till > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > >
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