I think Symbol.last seems like the best option so far, without breaking things.
On Fri, Jan 22, 2016 at 8:44 PM, John Gardner <[email protected]> wrote: > Using a well-known symbol to access an array's last element is probably > wiser than a typical method or property: > > let a = [0, 1, 2, 3]; > console.log( > a[Symbol.last] === 3 > /* true */ > ); > > There're obviously instances where authors have extended Array prototypes > with "last" methods or properties, but we can't guarantee they'd all work > the same. For instance, assume there are some implementations that skip > undefined values: > > var a = [0, 1, 2, undefined, undefined]; > Array.prototype.last = function(){ > return this[this.length - 1]; > }; > /** One that skips undefined values */ > Array.prototype.last = function(){ > var offset = 1; > while(offset < this.length && undefined === this[this.length - offset]) > ++offset; > return this[this.length - offset]; > } > > These discrepancies are subtle, but have the potential to break backwards > compatibility. > > Using a well-known symbol eliminates the potential for conflict. > Furthermore, it also offers an opportunity to complement any iterable > object's ability to synthesise array-like behaviour. For instance, it > enables iterables to also return the last object in their list of values: > > let pruebas = { > data: ["Probando", "la", "mierda", "esta", undefined], > > [Symbol.iterator](){ > /* Stuff with .data */ > }, > [Symbol.last](){ > /** Stuff to skip undefined values or whatever */ > let offset = 1; > let data = this.data; > while( > offset < data.length && > undefined === data[data.length - offset] > ) > ++offset; > return data[data.length - offset]; > } > } > > > On 23 January 2016 at 08:36, <[email protected]> wrote: >> >> Send es-discuss mailing list submissions to >> [email protected] >> >> To subscribe or unsubscribe via the World Wide Web, visit >> https://mail.mozilla.org/listinfo/es-discuss >> or, via email, send a message with subject or body 'help' to >> [email protected] >> >> You can reach the person managing the list at >> [email protected] >> >> When replying, please edit your Subject line so it is more specific >> than "Re: Contents of es-discuss digest..." >> >> Today's Topics: >> >> 1. Re: Javascript Language feature Idea (Bradley Meck) >> 2. Re: Re: Javascript Language feature Idea (Alican ?ubuk?uo?lu) >> 3. Re: Javascript Language feature Idea (kdex) >> 4. Re: Javascript Language feature Idea (kdex) >> 5. Re: Javascript Language feature Idea (Benoit Marchant) >> >> >> ---------- Forwarded message ---------- >> From: Bradley Meck <[email protected]> >> To: Dmitry Soshnikov <[email protected]> >> Cc: es-discuss <[email protected]> >> Date: Fri, 22 Jan 2016 13:51:54 -0600 >> Subject: Re: Javascript Language feature Idea >> Personally I prefer a well known symbol for marking you are grabbing from >> the end of the list rather than this wrapping behavior like D ( >> https://dlang.org/spec/arrays.html#array-length ). That said I think `.last` >> is more reasonable than changing prototypes. >> >> On Fri, Jan 22, 2016 at 1:17 PM, Dmitry Soshnikov >> <[email protected]> wrote: >>> >>> On Fri, Jan 22, 2016 at 9:53 AM, RacerD123 <[email protected]> wrote: >>>> >>>> In other programming languages such as python, you can specify the last >>>> element of a list with "list[-1]" but in javascript you have to do >>>> "list[list.length-1]". Is there maybe a way to make this feature in >>>> javascript? >>>> >>> >>> This could be a good addition, although `slice` may work as well. This >>> has been discussed previously as well in the last 4-5 years. In addition >>> with non-enumerable properties you can just monkey-patch `Array.prototype` >>> with the `peek` or `last` method. I guess approach when some library forces >>> some method to widely used, can be a good candidate for adding it to the >>> spec (this how it was with `Function.prototype.bind`, e.g., although today >>> monkey-patching is a bad practice of course). >>> >>> In addition, you can monkey-patch just `-1`, and other indexes, e.g. a >>> gist from 5 years old, when a similar topic was proposed here: >>> https://gist.github.com/DmitrySoshnikov/984921 >>> >>> Dmitry >>> >>> _______________________________________________ >>> es-discuss mailing list >>> [email protected] >>> https://mail.mozilla.org/listinfo/es-discuss >>> >> >> >> >> ---------- Forwarded message ---------- >> From: "Alican Çubukçuoğlu" <[email protected]> >> To: [email protected] >> Cc: >> Date: Fri, 22 Jan 2016 22:32:42 +0200 >> Subject: Re: Re: Javascript Language feature Idea >> More cool stuff: >> ```javascript >> const arr = [1, 2, 3]; >> >> // Easy push >> arr[] = 4; // => arr[arr.length]; >> >> // Easy s(p)lice >> arr[begin, end];, >> arr[begin,]; // => arr[begin, arr.length]; >> arr[begin, end] = [1, 2, 3]; >> ``` >> >> A terrible example (terrible because this should be done with WebGL >> shaders): >> ```javascript >> const image = [ /* Umbagajillion of RGBA pixels */ ]; >> >> function manipulate(rgba) { >> rgba[0] += 10; >> rgba[1] += 10; >> rgba[2] += 10; >> } >> >> for (let i = 0; i < image.length / 4; i++) { >> const begin = i * 4; >> const end = begin + 4; >> >> /* >> In case easy s(p)lice doesn't actually Array.p.slice >> and just creates a limited view of the array >> without breaking reference >> (image[begin, end] === image[begin, end]) >> */ >> manipulate(image[begin, end]); >> >> /* >> In case easy s(p)lice does Array.p.slice >> and creates a new array >> (image[begin, end] !== image[begin, end]) >> */ >> const pixel = image[begin, end]; >> manipulate(pixel); >> image[begin, end] = pixel; >> } >> ``` >> >> >> ---------- Forwarded message ---------- >> From: kdex <[email protected]> >> To: [email protected] >> Cc: >> Date: Fri, 22 Jan 2016 22:00:01 +0100 >> Subject: Re: Javascript Language feature Idea >> I really adore the slicing syntax. Just as a quick fix, though, >> > arr[begin,]; // => arr[begin, arr.length]; >> should obviously return `arr[begin, arr.length - 1]`. >> >> Honestly, I'm not too sure if the "easy push" syntax is particularly self- >> explanatory. There might be better alternatives. >> >> On Freitag, 22. Januar 2016 22:32:42 CET Alican Çubukçuoğlu wrote: >> > More cool stuff: >> > ```javascript >> > const arr = [1, 2, 3]; >> > >> > // Easy push >> > arr[] = 4; // => arr[arr.length]; >> > >> > // Easy s(p)lice >> > arr[begin, end];, >> > arr[begin,]; // => arr[begin, arr.length]; >> > arr[begin, end] = [1, 2, 3]; >> > ``` >> > >> > A terrible example (terrible because this should be done with WebGL >> > shaders): >> > ```javascript >> > const image = [ /* Umbagajillion of RGBA pixels */ ]; >> > >> > function manipulate(rgba) { >> > rgba[0] += 10; >> > rgba[1] += 10; >> > rgba[2] += 10; >> > } >> > >> > for (let i = 0; i < image.length / 4; i++) { >> > const begin = i * 4; >> > const end = begin + 4; >> > >> > /* >> > In case easy s(p)lice doesn't actually Array.p.slice >> > and just creates a limited view of the array >> > without breaking reference >> > (image[begin, end] === image[begin, end]) >> > */ >> > manipulate(image[begin, end]); >> > >> > /* >> > In case easy s(p)lice does Array.p.slice >> > and creates a new array >> > (image[begin, end] !== image[begin, end]) >> > */ >> > const pixel = image[begin, end]; >> > manipulate(pixel); >> > image[begin, end] = pixel; >> > } >> > ``` >> >> >> >> >> >> ---------- Forwarded message ---------- >> From: kdex <[email protected]> >> To: [email protected] >> Cc: >> Date: Fri, 22 Jan 2016 22:14:20 +0100 >> Subject: Re: Javascript Language feature Idea >> Standardizing unused array keys breaks compatibility about as much as >> extending the prototype does, really. Users can already mangle with both. >> >> The problems are a little more subtle, and yes, it would severely break >> backwards compatibility. Consider this example (accessing an element based >> on >> a computed index): >> >> ```js >> let a = [1, 2, 3]; >> let occurrence = a.indexOf(4); >> a[occurrence]; >> ``` >> >> Currently, this should result in `undefined`. After your proposal, you >> could >> introduce a potential bug into every program that accesses arrays using an >> index computed with `Array.prototype.indexOf`, since it would now return >> `3`. >> >> On Freitag, 22. Januar 2016 18:59:06 CET Sander Deryckere wrote: >> > Since Array inherits from Object, it can have any key, including the key >> > "-1". So something like list[-1] would break compatibility as users can >> > now >> > already assign values to the index -1. >> > >> > If you want a short way to access the last element, it should probably >> > be a >> > function in the Array prototype. Something like list.last(). >> > >> > Regards, >> > Sander >> > >> > 2016-01-22 18:53 GMT+01:00 RacerD123 <[email protected]>: >> > > In other programming languages such as python, you can specify the >> > > last >> > > element of a list with "list[-1]" but in javascript you have to do >> > > "list[list.length-1]". Is there maybe a way to make this feature in >> > > javascript? >> > > >> > > _______________________________________________ >> > > es-discuss mailing list >> > > [email protected] >> > > https://mail.mozilla.org/listinfo/es-discuss >> >> >> >> >> >> ---------- Forwarded message ---------- >> From: Benoit Marchant <[email protected]> >> To: kdex <[email protected]> >> Cc: [email protected] >> Date: Fri, 22 Jan 2016 13:35:55 -0800 >> Subject: Re: Javascript Language feature Idea >> Interesting! More pedestrian, it would be nice to finally have a version >> of splice that doesn't create a new other Array as a side effect. >> >> > On Jan 22, 2016, at 13:00, kdex <[email protected]> wrote: >> > >> > I really adore the slicing syntax. Just as a quick fix, though, >> >> arr[begin,]; // => arr[begin, arr.length]; >> > should obviously return `arr[begin, arr.length - 1]`. >> > >> > Honestly, I'm not too sure if the "easy push" syntax is particularly >> > self- >> > explanatory. There might be better alternatives. >> > >> >> On Freitag, 22. Januar 2016 22:32:42 CET Alican Çubukçuoğlu wrote: >> >> More cool stuff: >> >> ```javascript >> >> const arr = [1, 2, 3]; >> >> >> >> // Easy push >> >> arr[] = 4; // => arr[arr.length]; >> >> >> >> // Easy s(p)lice >> >> arr[begin, end];, >> >> arr[begin,]; // => arr[begin, arr.length]; >> >> arr[begin, end] = [1, 2, 3]; >> >> ``` >> >> >> >> A terrible example (terrible because this should be done with WebGL >> >> shaders): >> >> ```javascript >> >> const image = [ /* Umbagajillion of RGBA pixels */ ]; >> >> >> >> function manipulate(rgba) { >> >> rgba[0] += 10; >> >> rgba[1] += 10; >> >> rgba[2] += 10; >> >> } >> >> >> >> for (let i = 0; i < image.length / 4; i++) { >> >> const begin = i * 4; >> >> const end = begin + 4; >> >> >> >> /* >> >> In case easy s(p)lice doesn't actually Array.p.slice >> >> and just creates a limited view of the array >> >> without breaking reference >> >> (image[begin, end] === image[begin, end]) >> >> */ >> >> manipulate(image[begin, end]); >> >> >> >> /* >> >> In case easy s(p)lice does Array.p.slice >> >> and creates a new array >> >> (image[begin, end] !== image[begin, end]) >> >> */ >> >> const pixel = image[begin, end]; >> >> manipulate(pixel); >> >> image[begin, end] = pixel; >> >> } >> >> ``` >> > >> > >> > _______________________________________________ >> > es-discuss mailing list >> > [email protected] >> > https://mail.mozilla.org/listinfo/es-discuss >> >> >> _______________________________________________ >> es-discuss mailing list >> [email protected] >> https://mail.mozilla.org/listinfo/es-discuss >> > > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
