If you use yield instead of return in your generator function you'll get the desired results. When using a generator function to implement iteration, you'll generally want to avoid returning a final value, since for-of ignores the return value.
The return value does have an important role to play in coroutine-style use cases. On 2:20PM, Tue, Jun 30, 2015 Tim Jansen <[email protected]> wrote: > Hi, > > I am working on a collections library that supports the Iterable/Iterator > protocol, but I ran into a stumbling block: the iterator protocol seems to > work differently for arrays and generator functions. Array iterators set > 'done' to true *after* the last element, but function generators set 'done' > to true *on* the last element. > > Is this incompatibility intentional, or or just an implementation issue in > the browsers (tested on FF38 and Chrome 43)? I wasn't able to find any > information on this. The ES6 draft from April '15 doesn't define when > exactly 'done' is set. > > > Code example: > > var a = ['a', 'b']; > > var itA = a[Symbol.iterator]; > > itA.next(); // {value: 'a', done: false} > > itA.next(); // {value: 'b', done: false} !! > > itA.next(); // {value: undefined, done: true} > > > function* b() { > > yield 'a'; > > return 'b'; > > } > > var itB = a[Symbol.iterator]; > > itB.next(); // {value: 'a', done: false} > > itB.next(); // {value: 'b', done: true} !!! > > itB.next(); // {value: undefined, done: true} > > The difference is in the second invocation of next(), which returns true > for generator functions. That protocol makes it impossible for me to > support both generator functions and array iterators with the same > implementation - at least if I want to support 'undefined' as a valid value > in collections. I wouldn't be able to differentiate between an empty list > ([]) and a list containing undefined ([undefined]). > > > Thanks, > > Tim > > > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss >
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