Here is a PR for adding SliceExpression to proposal-slice-notation (that could probably be renamed proposal-slice-expression if it's accepted) https://github.com/tc39/proposal-slice-notation/pull/32
On Mon, Aug 19, 2019 at 10:29 AM Cyril Auburtin <cyril.aubur...@gmail.com> wrote: > I'd prefer to have it in slice-notation > https://github.com/tc39/proposal-slice-notation/issues/1#issuecomment-522227270 > > ```js > [...0:8] // [0,1,2,3,4,5,6,7] > ``` > > On Mon, Aug 19, 2019 at 9:34 AM Naveen Chawla <naveen.c...@gmail.com> > wrote: > >> I like it. I might prefer it in square brackets e.g. [ x ... y ] ? >> >> On Sun, 18 Aug 2019 at 23:24, Artem Kobzar <a.kobzar....@gmail.com> >> wrote: >> >>> ### Proposal: Range Expression >>> >>> The proposal based on one of the worst things in JavaScript Arrays. >>> >>> If i as developer want to make sequence of some numbers or characters >>> then i need to use weird methods like `Array.from`, manual filling or >>> imperative-style array filling. >>> >>> ```js >>> const group1 = [1, 2, 3, 4, 5, ...]// manual filling >>> const group2= Array.from({ length: 15 }).map((_, i) => i + 1); >>> const group3 = []; >>> for (let i = 0; i < 15; i++) group3[i] = i + 1; >>> ``` >>> >>> This ways to describe range sequence is huge and unreadable. >>> >>> >>> So, my proposal is: range expression which help to create lazy iterable >>> range sequence in declarative way. >>> >>> ```js >>> const group0 = 1...15; // from 1 to 15 >>> const group1 = 15...1; // from 15 to 1 >>> const group2 = 1n...15n // from 'a' to 'z' >>> const group3 = 'a'...'z' // from 'a' to 'z' >>> const group4 = 82... // lazy collection of numbers >>> >>> for (const odd of 1...85) { >>> // ... >>> } >>> >>> // in combination with https://github.com/tc39/proposal-iterator-helpers >>> const allEven = (1...100).filter(isEven); >>> ``` >>> >>> So, this operator is syntax sugar for the next generator which create >>> lazy iterable sequence: >>> >>> ```js >>> function* range(start, end, second) { >>> validate(start, end, second)// type assertion of start, second and end >>> const step = difference(start, second); // difference calculation >>> let current = start; >>> while(isNotEnd(current, end)) { // logic for negative step and >>> different types >>> yield current; >>> current = next(current, step); // function which change current >>> number | bigint | string by difference >>> } >>> } >>> ``` >>> _______________________________________________ >>> es-discuss mailing list >>> es-discuss@mozilla.org >>> https://mail.mozilla.org/listinfo/es-discuss >>> >> _______________________________________________ >> es-discuss mailing list >> es-discuss@mozilla.org >> https://mail.mozilla.org/listinfo/es-discuss >> >
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