> > > Hi James, > > I did alot of upgrading of javascript codebase to typescript code base > about 2 years ago for a year, where the goal was to get everything promised > and then basically > were possible ideally move to the await method. This required for us to > come up with peace meal approach were our codebase would have all forms and > for legacy integration of new code would have also gone back from a promise > to the callback. > I know we had a lot of fun and games with all different promise versions > and interface incompatibilities. At times was good enough to just > Promise.resolve(..promise) because that solve is matched in promise > BlueBird and ts promise implementations and things. > > What I can say is if you implement a wrapper function, whereby if the call > back is empty you return a promise and the type system typically would help > you out here. > > > https://github.com/wesleyolis/mongooseRelationalTypes/blob/master/src/mongoose.ts > > > > exec<TCallBack extends ((err: Error, res: QueryResultsDocumentModel< > TModelParts, Populate, DeepPopulate, ArrayOfResults, Primative, Lean>) => > void) | undefined> (callback: TCallBack): undefined extends TCallBack ? > Promise<QueryResultsDocumentModel<TModelParts, Populate, DeepPopulate, > ArrayOfResults, Primative, Lean>> : void; I also had to write my own > promise implementation, because we had some non-conformant callbacks, which > in which I had to get some results out on execution and not on the async > callback result. In this promise implementation I also typically, did some > optimizations, which depended on how many parameters one would pass in and > also the ordering of the terms because I wanted to make it more object > orientation, approach. The one thing which is not in here, which I wanted > is for the ability but I had push back is for if there where not additional > parameters to execute immediately, which is kinda not the best, because of > bit iffi. The other would have been that execute automatically, by you > passing in the additional parameters as auxiliary parameters after the > first two or one. const results = await Promisify(method)(param1, param2, > param3, param3); I get the fact that by calling promisify on a function > and that it then stores it in the parent scope (this) symbol, would save > overhead when having to do it alot. As the resulting function is > transformation is cached, however, one needs to remember that function name > is key in the prototype or instance method. So basically the key would be > the function name, then below that you would have two have another two > keys, one for the async symbol and one for the normal function. So either > the function name in my mind needs be suffix or prefix with symbol > convention or need to figure out how introduce some other mechanism. Is > possible mabye to overload await implementation, such that it can check for > the existence of Symbol, if it exists then it knows to call async version. > if it doesn't then it be call existing one. As of current the await, will > return the promise results or just the result of a function call. So you > could just replace that function entirely at the instance level too. Also > look at using promiseALL and doing shallow copies and then doing > promisifyALL on the shallow copy. > function promisify (test) { > > return async function() { > console.log('test'); > return test > } > } > > myFunction = promisify(myFunction); > > (async () => console.log(await myFunction('a','b')))(); > > https://github.com/wesleyolis/BlueBirdObjectOrientatedPromisification/blob/master/src/BlueBirdPromisification.ts > With > only a callback will execute the promise and return the result > > const result = await Promisify(method) > > > <https://github.com/wesleyolis/BlueBirdObjectOrientatedPromisification#with-mutiple-parameters-will-return-a-promisified-method>With > mutiple parameters will return a promisified method > > const promise = Promisify(method);const results = await promise(param1, > param2, param3, param3); > > > <https://github.com/wesleyolis/BlueBirdObjectOrientatedPromisification#object-and-method-instead-of-using-bluebird-context>Object > and Method, instead of using bluebird context > > Will ensure that the method key exists on the object. > > <https://github.com/wesleyolis/BlueBirdObjectOrientatedPromisification#with-only-a-callback-will-execute-the-promise-and-return-the-result-1>With > only a callback will execute the promise and return the result > > const result = await Promisify(object, 'method'); > > > <https://github.com/wesleyolis/BlueBirdObjectOrientatedPromisification#with-mutiple-parameters-will-return-a-promisified-method-1>With > mutiple parameters will return a promisified method > > const promise = Promisify(object, 'method');const results = await > promise(param1, param2, param3, param3); > > > <https://github.com/wesleyolis/BlueBirdObjectOrientatedPromisification#promises-return-type-can-also-be-overloaded>Promises > Return type can also be overloaded > > Requires spesifying both Promise Return type and callback method type. > > const promise = Promisify<{results : ''},(() => void)>(method); > > > <https://github.com/wesleyolis/BlueBirdObjectOrientatedPromisification#promise-with-returntype-some-weird-libaries>Promise > with ReturnType, some weird libaries. > > const promise = PromisifyReturn(...);let returnType = > {}promise(....,returnType); > console.log(returnType['executeResult']); > > > On Mon, Jun 22, 2020 at 9:21 PM James M Snell <jasn...@gmail.com> wrote: > >> For many legacy code bases that are based on callbacks mechanisms like >> node.js' promisify function are required to help facilitate the transition >> from callback centric code to Promise-centric. A lot of the time, these can >> follow straightforward rules without requiring customization. However, at >> other times it is necessary for user code to provide custom implementations >> of the Promise-version of the function. >> >> In Node.js, we accomplish this by allowing a function to have a symbol >> attached whose value is an alternative function that is returned by the >> promisify function >> >> For instance, >> >> function myFunction(foo, bar, callback) { >> callback(null, foo, bar); >> } >> myFunction[util.customPromisifySymbol] = async function(foo, bar) { >> return [foo, bar]; >> } >> >> const { promisify } = require('util'); >> const mine = promisify(myFunction); >> (async () => console.log(await mine('a','b')))(); >> >> As a convenience built into the language, it would be nice to be able to >> short-circuit the need to call promisify with a special language-level >> Symbol used specifically for this purpose: >> >> function myFunction(foo, bar, callback) { >> callback(null, foo, bar); >> } >> myFunction[Symbol.await] = async function(foo, bar) { >> return [foo, bar]; >> } >> >> (async () => console.log(await myFunction('a','b')))(); >> >> The idea here is that if the function being awaited has the >> [Symbol.await] property whose value is a function, then that function is >> called when the await keyword is used. That is, >> >> myFunction('a', 'b', callback); // Invokes myFunction directly >> await myFunction('a', 'b'); // Invokes myFunction[Symbol.await] >> >> if the Symbol.await property is not set or is not callable, then it would >> fallback to default behavior. >> >> Automatic handling of this binding should also happen but has some >> technical detail to work out: >> >> const obj = { >> a: 1, >> foo() {} >> }; >> obj.foo[Symbol.await] = async function() { >> return this.a; >> } >> await obj.foo(); // Calls await obj.foo[Symbol.await] with bound this >> >> This approach would make it far easier for legacy code bases to make the >> transition to async/await syntax while maintaining legacy compat. >> >> Before writing up a formal proposal, I wanted to solicit some feedback on >> this approach to see what folks thought. >> >> - James >> _______________________________________________ >> es-discuss mailing list >> es-discuss@mozilla.org >> https://mail.mozilla.org/listinfo/es-discuss >> > > > -- > ---- > GitHub:https://github.com/wesleyolis > LinkedIn:https://www.linkedin.com/in/wesley-walter-anton-oliver-85466613b/ > Blog/Website:https://sites.google.com/site/wiprogamming/Home > Skype: wezley_oliver > MSN messenger: wesley.o...@gmail.com >
-- ---- GitHub:https://github.com/wesleyolis LinkedIn:https://www.linkedin.com/in/wesley-walter-anton-oliver-85466613b/ Blog/Website:https://sites.google.com/site/wiprogamming/Home Skype: wezley_oliver MSN messenger: wesley.o...@gmail.com
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