es6-promise

问题 I have the following code: new Promise((resolve, reject) => { resolve(1) }).then(value => { return 2 }) I resolve the initial promise with 1 . Then in the then block I do return 2 . Does this return a promise resolved with the value 2? 回答1: Yes. Calling .then creates a new promise, and that promise will resolve to whatever you return in the callback. 来源： https://stackoverflow.com/questions/61510453/js-promises-is-doing-returnvalue-in-a-then-block-the-same-as-resolving

问题 I am trying to export a firestore function that performs a query and returns an array containing the objects in that query. I am trying to get data from a subcollection of a document, and get an array of document objects returned to render to the client. I've tried the below but it's not working (e.g. the object returns blank). I think this has to do with improper handling of promises, but couldn't figure it out on my own. Thanks for your help. export const getEvents = (id) => { let events =

问题 Angular2 has very useful promises error catching mechanism for chained promises. Yet, the usual case (at least for me) is that of promises called from within the resolve handler of the previous one. This is due to the need to process information prior to starting the next promise. For example: this.d( "facebookOAuthLogin() - starts" ); this.fbProvider.login().then( ( loginResponse: { status: string, authResponse: any, accessToken: string, expiresIn: string, session_key: string, sig: string,

问题 Angular2 has very useful promises error catching mechanism for chained promises. Yet, the usual case (at least for me) is that of promises called from within the resolve handler of the previous one. This is due to the need to process information prior to starting the next promise. For example: this.d( "facebookOAuthLogin() - starts" ); this.fbProvider.login().then( ( loginResponse: { status: string, authResponse: any, accessToken: string, expiresIn: string, session_key: string, sig: string,

问题 I have already gone through the thread Any difference between await Promise.all() and multiple await?, so I am clear about Promise.all and multiple awaits. Still, I am not very clear about the below 2 scenarios. In Case 1 why does it execute sequentially (takes 10s) whereas in Case 2 it executes in parallel (takes 4s)? Case 1: function promiseWait(time) { return new Promise((resolve, reject) => { setTimeout(() => { resolve(true); }, time); }); } async function test1() { var t0 = performance

问题 If a promise is created this way: myPromise = new Promise(function(resolve, reject) {}); Can this promise be ever resolved by any way? Obviously, the executor is not resolving it in this case, so can the promise be ever resolved? I think if it is jQuery, it can be resolved by deferred.resolve() so that the related promise deferred.promise() is resolved. 回答1: No, the promise can only be resolved or rejected by the resolve and reject functions, respectively. If these functions aren't called nor

问题 If a promise is created this way: myPromise = new Promise(function(resolve, reject) {}); Can this promise be ever resolved by any way? Obviously, the executor is not resolving it in this case, so can the promise be ever resolved? I think if it is jQuery, it can be resolved by deferred.resolve() so that the related promise deferred.promise() is resolved. 回答1: No, the promise can only be resolved or rejected by the resolve and reject functions, respectively. If these functions aren't called nor

问题 I have the following code: var incr = num => new Promise(resolve => { resolve(num + 1); }); var x = incr(3) .then(resp => incr(resp)) .then(resp => console.log(resp)); async function incrTwice(num) { const first = await incr(num); const twice = await incr(first); console.log(twice); } incrTwice(6); Which I believe (perhaps mistakenly) shows two equivalent ways to achieve the same functionality: first by chaining promises and second with the syntactic sugar of async/await. I would expect the

问题 So I have a problem with JavaScript Promises. I'm using native implementation for the sake of reducing dependencies. An illustrative example of what I need. I need to retrieve lists of books, book authors and purchases. I also need an author profile for each of the authors. After I got all of that, I need to create a nice set of Authors with their books and purchase list for each of the books. Lists and profiles are separate API JSON calls. The only dependency is that I need a list of authors

问题 So I have a problem with JavaScript Promises. I'm using native implementation for the sake of reducing dependencies. An illustrative example of what I need. I need to retrieve lists of books, book authors and purchases. I also need an author profile for each of the authors. After I got all of that, I need to create a nice set of Authors with their books and purchase list for each of the books. Lists and profiles are separate API JSON calls. The only dependency is that I need a list of authors