https://onp4.com/@vadim/~js JavaScript Thu, 14 May 2026 08:23:59 GMT https://validator.w3.org/feed/docs/rss2.html P4 - P for posting en Copyright, P4 https://onp4.com/@vadim/p/ut31o77l9x https://onp4.com/@vadim/p/ut31o77l9x Sun, 19 Oct 2025 22:38:04 GMT https://onp4.com/@vadim/p/0ic41fxln8 https://onp4.com/@vadim/p/0ic41fxln8 Fri, 29 Aug 2025 09:39:27 GMT https://onp4.com/@vadim/p/tqziv1amkg https://onp4.com/@vadim/p/tqziv1amkg Wed, 30 Jul 2025 08:41:44 GMT { // Code block ... })()); } } ```]]> https://onp4.com/@vadim/p/97awamfsgw https://onp4.com/@vadim/p/97awamfsgw Fri, 11 Jul 2025 18:36:25 GMT https://onp4.com/@vadim/p/01h774oe2i https://onp4.com/@vadim/p/01h774oe2i Mon, 16 Jun 2025 09:53:36 GMT https://onp4.com/@vadim/p/swwz2wfdj3 https://onp4.com/@vadim/p/swwz2wfdj3 Wed, 19 Mar 2025 18:32:08 GMT https://onp4.com/@vadim/p/lly1bbudbd https://onp4.com/@vadim/p/lly1bbudbd Sat, 16 Nov 2024 21:52:29 GMT [...document.querySelectorAll('*')] .forEach(e => e.style.outline = '1px dotted red') , 1000) ``` ]]> https://onp4.com/@vadim/p/20266uv7pf https://onp4.com/@vadim/p/20266uv7pf Wed, 23 Oct 2024 13:25:57 GMT https://onp4.com/@vadim/p/kl0ses006y https://onp4.com/@vadim/p/kl0ses006y Tue, 08 Oct 2024 18:07:26 GMT https://onp4.com/@vadim/p/rnp76a72lm https://onp4.com/@vadim/p/rnp76a72lm Fri, 23 Aug 2024 13:20:23 GMT = | (error: E) => void; | (error: void, value: V) => void; ``` The new *CallbackAwaitExpression* would have an extra **identifier** parameter of type `Callback`, syntactically in between the `await` keyword and the expression being awaited, for example, note the `cb` identifier: ```js await cb fs.readFile('myfile.txt', 'utf-8', cb); ``` Likewise, the async function syntax would also be extended to allow *AsyncCallbackFunction* type. There as well, the syntax would allow a single callback identifier: ```js async cb function(args, cb) { // ... } ``` Putting this all together, this would allow to write async/await syntax-powered code, while benefiting from the performance of callbacks. It would allow to write code like this: ```js async _ function getFileData(filename, _) { try { const data = await _ fs.readFile('myfile.txt', 'utf-8', _); return 'mydata: ' + data; } catch (error) { if (!!error && typeof error === 'object' && error.code === 'ENOENT') { throw new Error('not found'); } throw error; } } ``` The code would be equivalent to the existing JavaScript: ```js function getFileData(filename, callback) { const onCatch = (error) => { if (!!error && typeof error === 'object' && error.code === 'ENOENT') { callback(new Error('not found')); } else { callback(error); } }; try { fs.readFile('myfile.txt', 'utf-8', (err, data) => { if (err) { onCatch(err); } else { try { callback(null, 'mydata: ' + data); } catch (error) { onCatch(error); } } }); } catch (error) { onCatch(error); } } ``` Here is how the above code can look like using the existing async/await syntax. The code is almost equivalent to the *async/await callback* proposal, but less performant due to `Promise` usage. ```js async function getFileDataAsync(filename) { try { const data = await promisify(fs.readFile)('myfile.txt', 'utf-8'); return 'mydata: ' + data; } catch (error) { if (!!error && typeof error === 'object' && error.code === 'ENOENT') { throw new Error('not found'); } throw error; } } ``` Or, equivalently, the good old `promisify` utility could convert our callback powered function to this `Promise` powered one: ```js const getFileDataAsync = promisify(getFileData); ``` ## Sugar Syntax When awaiting one can explicitly specify the callback identifier and explicitly use it as an argument: ```js await myCallback fs.readFile('a.txt', myCallback) ``` If the await identifier `myCallback` is not used, it is automatically inserted in the function call as the last argument: ```js await _ fs.readFile('a.txt') ``` When defining an async callback function, the above text proposed to explicitly specify the callback identifier, like so: ```js async myCallback function getData(filename, myCallback) {} ``` Instead it can be reduced by simply using the `async` keyword once, in place of some argument: ```js function getData(filename, async) {} ``` The above syntax modifications reduce the example `getFileData` function to the following: ```js function getFileData(filename, async) { try { const data = await _ fs.readFile('myfile.txt', 'utf-8'); return 'mydata: ' + data; } catch (error) { // ... } } ``` ## Using with TypeScript From the point of view of TypeScript, to define a new async callback function, one can simply use the `CallbackType`: ```ts type GetFileData = (filename: string, callback: Callback) => void; ``` Alternatively, the `async` type shorthand could be introduced, to make it more explicit: ```ts type GetFileData = (filename: string, async) => void; ``` Maybe it could be called `callback`: ```ts type GetFileData = (filename: string, callback) => void; ``` ]]> https://onp4.com/@vadim/p/gqrahqqvms https://onp4.com/@vadim/p/gqrahqqvms Sun, 18 Aug 2024 08:51:39 GMT = ErrorCallback | ValueCallback; type ErrorCallback = (error: E) => void; type ValueCallback = (error: void, value: V) => void; ``` The new *CallbackAwaitExpression* would have an extra **identifier** parameter of type `Callback`, syntactically in between the `await` keyword and the expression being awaited, for example, note the `cb` identifier: ```js await cb fs.readFile('myfile.txt', 'utf-8', cb); ``` Likewise, the async function syntax would also be extended allow *AsyncCallbackFunction* type. There as well, the syntax would allow a single callback identifier: ```js async cb function(args, cb) { // ... } ``` Putting this all together, this would allow to write async/await syntax-powered code, while benefiting from the performance of callbacks. It would allow to write functions like: ```js async _ function getFileData(filename, _) { try { const data = await _ fs.readFile('myfile.txt', 'utf-8', _); return 'mydata: ' + data; } catch (error) { if (!!error && typeof error === 'object' && error.code === 'ENOENT') { throw new Error('not found'); } throw error; } } ``` The code would be equivalent to the existing JavaScript: ```js function getFileData(filename, callback) { const onCatch = (error) => { if (!!error && typeof error === 'object' && error.code === 'ENOENT') { callback(new Error('not found')); } callback(error); }; try { fs.readFile('myfile.txt', 'utf-8', (err, data) => { if (err) return onCatch(err); callback(null, 'mydata: ' + data); }); } catch (error) { onCatch(error); } } ``` Here is how the above code can look like using the existing async/await syntax. The code is almost equivalent to the *async/await callback* proposal, but less performant due to `Promise` usage. ```js async function getFileData(filename) { try { const data = await promisify(fs.readFile('myfile.txt', 'utf-8')); return 'mydata: ' + data; } catch (error) { if (!!error && typeof error === 'object' && error.code === 'ENOENT') { throw new Error('not found'); } throw error; } } ```]]> https://onp4.com/@vadim/p/857h4ap4ls https://onp4.com/@vadim/p/857h4ap4ls Thu, 08 Aug 2024 19:07:09 GMT https://onp4.com/@vadim/p/ehvyvq5g6w https://onp4.com/@vadim/p/ehvyvq5g6w Sun, 16 Jun 2024 22:14:34 GMT https://onp4.com/@vadim/p/0pshojgkpq https://onp4.com/@vadim/p/0pshojgkpq Fri, 14 Jun 2024 12:02:16 GMT https://onp4.com/@vadim/p/eaw42510se https://onp4.com/@vadim/p/eaw42510se Fri, 14 Jun 2024 12:01:27 GMT https://onp4.com/@vadim/p/vxuibqku5g https://onp4.com/@vadim/p/vxuibqku5g Mon, 13 May 2024 22:18:54 GMT https://onp4.com/@vadim/p/dqnx8upmvk https://onp4.com/@vadim/p/dqnx8upmvk Mon, 13 May 2024 22:18:43 GMT https://onp4.com/@vadim/p/7ie0x9pzmm https://onp4.com/@vadim/p/7ie0x9pzmm Sat, 11 May 2024 10:48:57 GMT https://onp4.com/@vadim/p/t9gm6knczt https://onp4.com/@vadim/p/t9gm6knczt Wed, 03 Apr 2024 11:41:41 GMT a.src) ```]]> https://onp4.com/@vadim/p/af3n8t9yk6 https://onp4.com/@vadim/p/af3n8t9yk6 Mon, 04 Mar 2024 14:44:12 GMT https://onp4.com/@vadim/p/gi6f3adu0v https://onp4.com/@vadim/p/gi6f3adu0v Sun, 03 Mar 2024 19:51:28 GMT https://onp4.com/@vadim/p/fmuxmxaysp https://onp4.com/@vadim/p/fmuxmxaysp Wed, 16 Aug 2023 21:59:56 GMT https://onp4.com/@vadim/p/elnqp3roc7 https://onp4.com/@vadim/p/elnqp3roc7 Sat, 08 Jul 2023 22:22:29 GMT https://onp4.com/@vadim/p/axuothg11o https://onp4.com/@vadim/p/axuothg11o Fri, 07 Jul 2023 07:32:57 GMT https://onp4.com/@vadim/p/nl9jcosg43 https://onp4.com/@vadim/p/nl9jcosg43 Tue, 13 Jun 2023 11:45:15 GMT https://onp4.com/@vadim/p/tjto7dj6jc https://onp4.com/@vadim/p/tjto7dj6jc Mon, 24 Apr 2023 20:07:29 GMT https://onp4.com/@vadim/p/dlpkxvvt3h https://onp4.com/@vadim/p/dlpkxvvt3h Wed, 19 Apr 2023 21:48:11 GMT https://onp4.com/@vadim/p/6hhelfqdaw https://onp4.com/@vadim/p/6hhelfqdaw Wed, 19 Apr 2023 19:20:44 GMT https://onp4.com/@vadim/p/nvppvgm38b https://onp4.com/@vadim/p/nvppvgm38b Fri, 14 Apr 2023 15:57:29 GMT https://onp4.com/@vadim/p/6hr87w1xdr https://onp4.com/@vadim/p/6hr87w1xdr Sun, 09 Apr 2023 21:34:44 GMT 0); ```]]>