That would create a refactoring hazard if i had the block: `{ a(); b();
return c(); }` and stuck the `async` keyword in front of it - suddenly the
function wouldn't have an early completion in the block, it'd create and
throw away a Promise.On Tue, Jan 3, 2017 at 12:52 AM, Igor Baklan <[email protected]> wrote: > I looks like it would be nice to have ``async``-block which might be alias > to ``async``-lambda immediate invocation, so that: > > ```js > var promise = async { /*some statements with await*/ }; > ``` > <==> > > ```js > var promise = (async () => { /*some statements with await*/ }) (); > ``` > > and > > ```js > var promise = async ( /*some statements with await*/ ); > ``` > <==> > > ```js > var promise = (async () => ( /*some expression with await*/ )) (); > ``` > > Then it can gave some convenience in writing some semi-async function, > like for example parallel async batch processing, which might look like: > > ```js > const backupBatch = (batch) => { > var tasks = []; > for (let item of batch) { > tasks.push( > async { > const content = await readContent(item); > await writeContent(item + ".bak", content); > } > ) > } > return Promise.all(tasks) > } > ``` > > or like > > ```js > const backupBatch = (batch) => { > var tasks = []; > for (let item of batch) { > tasks.push( > async ( > await writeContent(item + ".bak", await readContent(item)); > ) > ) > } > return Promise.all(tasks) > } > ``` > > of course this simplistic case can be rewritten without ``async``-block > like: > > ```js > const backupBatch = (batch) => { > return Promise.all( > batch.map( > async (item) => ( > await writeContent(item + ".bak", await readContent(item)); > ) > ) > ); > } > ``` > However I believe this not reduce usefulness of initial ``async``-block > construction. > > Also it should be mentioned that this idea "is't new", something very > similar I saw in [[async-do]](/topic/support-syntax#content-5) comment. > > And finally, if this construct will be introduced, it will provide some > nice symmetry - of whether you put async keyword in function header > definition, or at the very beginning of its body, like: > > ```js > const asyncFunc = async (/*args*/) => {/*function body with await-s*/}; > ``` > <==> > ```js > const asyncFunc = (/*args*/) => { return async {/*function body with > await-s*/} }; > ``` > <==> > ```js > const asyncFunc = (/*args*/) => ( async {/*function body with await-s*/} ); > ``` > > And > ```js > const asyncFunc = async (args) => (some_async_expression); > ``` > <==> > ```js > const asyncFunc = (args) => async (some_async_expression); > ``` > > By the way parentheses here is essential, since ``async x => x`` != > ``async (x => x)``, cause first evaluates into async-function, while the > second should be evaluated into completed promise which value is ``sync`` > function ``(x => x)``. > > > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss > >
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