I will pass your good arguments to the spec author. Personally I am not in strong favor of mimicking Array.slice. I just found the problems we have during implementation and seek the solution.
On Fri, Apr 22, 2011 at 3:00 PM, Geoffrey Garen <gga...@apple.com> wrote: > I would suggest updating the specification for Blob.slice() so that it >> doesn't expect passing "undefined" for the second argument to have >> identical behavior to not passing the argument at all. The "subarray" >> method in the Typed Array spec [1], which has similar behavior to >> slice(), doesn't mention the undefined value. >> > > I am afraid that this suggested change might not be preferred since we're > trying to mimic the behavior of Blob.slice to Array.slice and Array.slice > does allow passing undefined and treat it as omitting the value. > > > Jian, > > Can you clarify why we want Blob.slice to mimic Array.prototype.slice in > this strange argument quirk? > > Let me suggest three reasons why we don't want Blob.slice to mimic > Array.prototype.slice in this strange argument quirk: > > 1. Legacy argument quirks exist for legacy compatibility and nothing else. > Since Blobs have no legacy requirements, they should not re-introduce the > mistakes of JavaScript past. There are many legacy argument quirks in > JavaScript. They often confuse programmers, rather than enabling them. For > example, new Array(x) creates an array with ToInteger(x) elements in it, > while new Array(x, y) creates an array with 2 elements in it, x and y. Would > you mimic that quirk in Blobs if you could? > > 2. A Blob is not an Array. Blobs are incompatible with all other Array > semantics. They don't have a length property. They don't support bracket > access. They don't support destructive modification. If Blobs were like > Arrays, you could just use Array.prototype.slice to slice a Blob. But you > can't, because they're not alike at all. > > 3. Your specification doesn't actually conform to the exact semantics of > all the argument quirks of Array.prototype.slice. There are a number of > other quirks that you have left out because they are strange and you are not > familiar with them. I will leave it as a thought experiment for you to go > and find all the other quirks of Array.prototype.slice that you have missed. > While you are seeking them out, you can meditate on whether you are making > your API better or worse. > > Geoff >
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