Detailed explanation of promise object in Angularjs

This time I will bring you a detailed explanation of the promise object of Angularjs. What are the precautions when using the promise object of Angularjs? The following is a practical case, let's take a look.

What is promise? To understand it, we need to start with the problem we face. When operating ajax asynchronous requests, you must add a callback function to handle the logic after the request is successful, but this method is at the expense of control flow, Exception handling, and may also fall into the callback In nested functions, the process is complex and the code is bloated. In angularjs, when dealing with asynchronous processing, we may first think of using $watch listeners to implement it, but too many listeners will affect performance and the code structure will be messy.

In order to solve this situation, the concept of promise object is introduced in Angularjs. To be precise, it is an elegant mode for handling asynchronous programming, which can effectively solve Callback function tedious and handle business processes in a synchronous manner. At the same time, chain writing is allowed in callbacks. Next, we will explain in detail how to use the promise object:

Basic concepts of promise and usage methods

1. In order To explain the concept of promise more vividly and learn more about its

attributes and methods , here we use an example to compare and describe. For example: A customer named A asked a company named B to develop a WEB page. Company B promised to complete it in three days. This promise is a promise object, which is essentially initiated by customer A. Deferred business, in Angular, we can understand it as the process of creating a deferred object by calling the defer method on the $q object.

2. In the next three days, the customer may communicate with the company about the development progress, which can be understood as calling the notify method of the deferred object

Send a message# The process of ## indicates that the status of this deferred business is "unfinished or in progress"; if after three days, Company B normally delivers the page developed by Customer A, it can be understood as calling the resolve method process indicates that the status of this deferred business is "completed"; and if company B finds that it cannot be implemented during the production process, customer A cannot deliver, which can be understood as calling the deferred object The process of the reject method indicates that the status of this deferred business is "unable to be completed". 3. When Company B receives a demand from Customer A, it discovers that a project it has done before is completely consistent with its current needs, and decides to give the previously completed project directly to Company B. The customer will also be very satisfied. In this case, no deferred business is generated, so it can be understood as the process of calling the when method through the $q object.

4. Through this example, we can see from the group that neither customer A nor company B has much time for each other, and the process is very common. This is an important feature of the promise object. In addition, from the example we vividly understand the creation process of the promise object. As well as the functions represented by defer(), notify(), reject(), and when() methods.

Below, we will introduce the creation process of promise objects. If you want to create a promise object in Angular, you must first inject the $q service into the template, and first call the defer method to create a deferred object. The code is as follows:

angular.module("a",[])
  .controller("c",["$scope","$q",function($scope,$q){  var defer=$q.defer();
}])

I believe you have mastered the method after reading the case in this article. , for more exciting content, please pay attention to other related articles on the php Chinese website!

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