The Ionic framework has a defined variable

In my code, I have initialized a variable inside the constructor like this:

constructor(public http: HttpClient) {
    this.data = null;
    this.http.get(this.url).subscribe((datas: any) => {
      this.dbUrl = datas[0].db_url2;
      console.log(this.dbUrl) // <- output here
    })
  }

The output that I see is:

987456321

Later, in a different method within the same class, I reference the variable again:

getDetails() {
    let headers = new HttpHeaders();
    headers.append('Content-Type','application/json');
    console.log(this.dbUrl); // <- expected output here
    return this.http.get(this.dbUrl + 'details', { headers: headers})

  }

However, when I try to display the output, it shows as Undefined. The dbUrl is declared as a global variable. Can anyone assist me with solving this issue?

Answer №1

The initial part of your code involves making an HTTP call, which subscribes to an Observable. This means that the result is not returned immediately (due to it being a web request) and instead observes changes in the http.get method.

In the subsequent part of the code, you're logging the value of dbUrl. However, the code executes faster than the time required for the app to complete the request. As a result, dbUrl is not defined in the second log due to:

1) dbUrl is not yet defined
2) The http.get function is waiting for a response from the server
3) You call getDetails and log dbUrl, which is currently null
4) After receiving a response from the server, dbUrl is then set

To address this issue, consider following these steps:

// Define a method to retrieve the dbUrl asynchronously using a promise.
getUrl(){
    return new Promise<any>(
    function (resolve, reject) {
      this.http.get(this.url).subscribe((datas: any) => {
        this.dbUrl = datas[0].db_url2;
        resolve(this.dbUrl);
      }
}

Next, update your getDetails method as follows:

getDetails() {
    // Check if dbUrl has been initialized
    if(this.dbUrl == undefined){
          this.getUrl()
          .then(url => {
            this.dbUrl = url;
            this.getDetails();
           })
          .catch(error => console.log(error))
        })
    }else{
        let headers = new HttpHeaders();
        headers.append('Content-Type','application/json');
        return this.http.get(this.dbUrl + 'details', { headers: headers})
    }
}

When calling getDetails, if dbUlr is not yet available, it will wait for its initialization before recursively calling getDails and executing the request.

Similar questions

If you have not found the answer to your question or you are interested in this topic, then look at other similar questions below or use the search

software tool for managing state transitions

Can anyone recommend a superior javascript library for workflows? Right now, I'm utilizing Joint JS, but I require something with a more visually appealing interface (users tend to prefer that). ...

Javascript generates a mapping of values contained within an array

In my current project, I am developing a feature that allows users to create customizable email templates with placeholder tags for content. These tags are structured like [FirstName] [LastName]. My goal is to brainstorm the most effective method for crea ...

An HTML attribute with a blank value will not display the equals sign operator

jQuery can be used like this: $select.append('<option value="">All</option>'); This code appears to insert the element in HTML as follows: <option value>All</option> However, what is intended is to append the elemen ...

What are the steps for integrating Socket.IO into NUXT 3?

I am in search of a solution to integrate Socket.IO with my Nuxt 3 application. My requirement is for the Nuxt app and the Socket.IO server to operate on the same port, and for the Socket.IO server to automatically initiate as soon as the Nuxt app is ready ...

Is there a way to create an <a> element so that clicking on it does not update the URL in the address bar?

Within my JSP, there is an anchor tag that looks like this: <a href="patient/tools.do?Id=<%=mp.get("FROM_RANGE") %>"> <%= mp.get("DESCRITPION") %></a>. Whenever I click on the anchor tag, the URL appears in the Address bar. How can ...

The PropertyOverrideConfigurer encountered an issue while processing the key 'dataSource' - The key 'dataSource' is invalid, it was expecting 'beanName.property'

During the installation of Sailpoint on Oracle, the configuration properties are as follows: ##### Data Source Properties ##### dataSource.maxWaitMillis=10000 dataSource.maxTotal=50 dataSource.minIdle=5 #dataSource.minEvictableIdleTimeMillis=300000 #dataSo ...

Updating Angular 8 Component and invoking ngOninit

Within my main component, I have 2 nested components. Each of these components contain forms with input fields and span elements. Users can edit the form by clicking on an edit button, or cancel the editing process using a cancel button. However, I need to ...

Issue with saving date values accurately in Nestjs/Prisma

After logging the response body before saving it to the database, I noticed that the shape is correct. Here's what it looks like: //console.log response body CreateOpenHourDto { day: 'WEDNESDAY', startTime: 1663858800000, endTime: 16638786 ...

What steps can be taken to resolve the issue of receiving the error message "Invalid 'code' in request" from Discord OAuth2?

I'm in the process of developing an authentication application, but I keep encountering the error message Invalid "code" in request when attempting to obtain a refresh token from the code provided by Discord. Below is a snippet of my reques ...

Enhancing data management with Vuex and Firebase database integration

Within my app, I am utilizing Firebase alongside Vuex. One particular action in Vuex looks like this: async deleteTodo({ commit }, id) { await fbs.database().ref(`/todolist/${store.state.auth.userId}/${id}`) .remove() .then ...

Payload bytes do not match the expected byte values

I am facing an issue where the image data sent by the user is getting saved on the server in a corrupt state. Here is the structure of my setup: - api . index.js - methods . users.js (I have omitted unrelated files) There is a server.js outside ...

Struggling to figure out how to change the display when navigating between different routes

I've been struggling for the past 3 hours trying to switch between routes. Let me explain further: Server Template HTML: <!-- I want the first div to display when the component opens, but disappear and show router-outlet when a button is clicked. ...

How can you prevent a draggable element from surpassing the bottom of the screen?

I'm dealing with an element that I want to make draggable only along the Y-axis. It needs to be able to go past the top of the screen, but I need to restrict it from going past the bottom of the screen. I recently came across the containment feature i ...

Retrieve a specific nested key using its name

I am working with the following structure: const config = { modules: [ { debug: true }, { test: false } ] } My goal is to create a function that can provide the status of a specific module. For example: getStatus("debug") While I can access the array ...

Combine several objects into one consolidated object

Is there a way to combine multiple Json objects into one single object? When parsing an array from AJAX, I noticed that it logs like this: 0:{id: "24", user: "Joe", pass: "pass", name: "Joe Bloggs", role: "Technical Support", ...} 1:{id: "25", user: "Jim ...

Tips for preventing the ng-click event of a table row from being triggered when you specifically want to activate the ng-click event of a checkbox

So, I've got this situation where when clicking on a Table Row, it opens a modal thanks to ng-click. <tr ng-repeat="cpPortfolioItem in cpPortfolioTitles" ng-click="viewIndividualDetailsByTitle(cpPortfolioItem)"> But now, there&apos ...

The variable (form.onsubmit) remains unset even after assigning a value

function setFormOnSubmit(formName){ if(!formName) return; var form = document[formName]; form.onsubmit = function(){ console.log('This is the onsubmit function'); }; console.log('onsubmit successfully set ...

Implementing a secure route in Next.js by utilizing a JWT token obtained from a customized backend system

Currently, I am in the process of developing a full-stack application utilizing NestJS for the backend and Next.js for the frontend. Within my NestJS backend, I have implemented stateless authentication using jwt and passport. My next goal is to establis ...

Assigning nested JSON values using Jquery

My JSON data structure is as follows: { "Market": 0, "Marketer": null, "Notes": null, "SalesChannel": null, "ServiceLocations": [ { "ExtensionData": null, "AdminFee": 0, "CommodityType": 0, ...