js promise

In node. js, q. js is used to implement api promise. node. jsq. js About what is promise and promise solution is what problem, please experience node callback asynchronous encoding method, along with the step http://wiki.commonjs.

This article mainly introduces node. use q. js implements api promise. promise is a standard that describes the returned results of asynchronous calls, including correct returned results and error handling, need a friend can refer to what is promise and promise solution is w

This article describes how to use Promise in Node. js to encapsulate asynchronous functions and use unified chained APIs to get rid of the nightmare of multiple callbacks. it is a very practical little skill, I hope my friends will like writing Node. during the js process, continuous IO operations may lead to "pyramid nightmare". the multiple nesting of callback

functions are called, in addition, a promise can even accept a new callback after the implementation is resolved. These callbacks are done in a normal way, allowing us to use callbacks to implement a simple form of caching:vartaskspromise;functiongettasks () {taskpromise= Taskpromise | |Gettasksfromtheserver (); returnTaskpromise;} In this case, the Gettasks () function can be called any number of times, and it always returns the

PromiseThe motives for studying Promise are broadly as follows: Unfamiliar with its API and curiosity about the implementation mechanism; Many libraries (such as fetch) are based on the Promise package, so to understand the preconditions of these libraries first familiar with Promise; To understand other more advanced asynchronous operations to b

It's enough to talk about js promise. It's enough to talk about jspromise. I. background We all know that nodejs is very fast. Why is it so fast? The reason is that node uses asynchronous callback to process the events that need to be waited, so that the Code will continue to be executed without waiting somewhere. But there is also a bad thing. When we have a lot of callbacks, for example, after the callbac

second parameter of then, used to specify the callback of the reject, the usage is this:GetNumber (). Then (function (data) { Console.log (' resolved '); Console.log (data);}). catch (function (reason) { console.log (' rejected '); Console.log (reason);});The effect is the same as the second parameter written in then. However, it has another function: When executing the resolve callback (that is, the first argument in the above then), if the exception is thrown (the code is wrong),

* Promise Commitment* Solve the problem of asynchronous programming in JS** Asynchronous-synchronous* Blocking-no blocking** What is the difference between synchronous and asynchronous? Synchronous refers to the mechanism by which the requested person (the handler of the thing) is notified when it is done. Async: When the event is completed, the requestor sends a message informing the requestor that the tra

of the Resolve method do not have a specific rule, basically put the parameters to be passed to the callback function in it. (then the method can receive this parameter value)6.promise.resolveIn general we will use new Promise () to create Promise objects, but we can use other methods as well. Here promise.resolve is used for example: New Promise (function (Reso

Use q. js in node. js to implement api promise Here we will look at how to use q. js to implement node api promise. 　　I. Everything starts with install The Code is as follows: Npm install q 　　Ii. Standard node style api promise Me

Mode", these 4 methods can write more reasonable structure, better performance, maintenance more convenient JS code. These four modes are:First, the callback function (callback);Second, event monitoring (Listener);Third, the observer model;Iv. Promise ObjectsFirst, callback function (callback)The most basic method of asyncSuppose there are two functions, F1 and F2, which wait for the former to execute the

Deep understanding of js promise chain and promisechain Native Promise is added to the new standard. Here we will only discuss the use of the chain, and think about the details. I. Review of then () and catch () The callback function can be placed in the parameters of then () and catch () to receive the final result of a Prom