The created function in VueJS may sometimes result in an undefined outcome

Question

The created function in VueJS may sometimes result in an undefined outcome

I recently started a project with VueJs where I encountered an issue while making a GET request using the Axios library. The data was returned as expected, but I faced difficulties calling the loadUsers function inside mounted. Here is my code snippet:

export default{
  data(){
     return {
        users : {}
     }
  },
  methods:{
     addCustomer(){
        var formData = $('#add-customer').serialize();
        axios.post('/Thirdparty', formData).then(function(response){
           helper.validation(response.data);
        });
     },
     loadUsers(){
        axios.get('/Thirdparty/loadUsers').then(function(data){
           this.users = data.data;
        });
     }
  },
  created(){
     let self=this
     self.loadUsers(); 
  }
}

Despite using the 'self' variable to call the loadUsers() function, I still encountered the error stating that 'this' is undefined.

javascript vue.js axios

Answer 1

Answer №1

When you reference this.users within the callback to axios.get().then() in the function loadUsers(), be mindful that using a standard function instead of an arrow function can cause unexpected behavior. In this case, this does not refer to the Vue instance as intended, leading to scope issues. To resolve this, either switch to an arrow function or adjust the way you reference this:

// Option 1 - Use an arrow function
export default{
  data(){
     return {
        users : {}
     }
  },
  methods:{
     addCustomer(){
        var formData = $('#add-customer').serialize();
        axios.post('/Thirdparty', formData).then((response) => {
           helper.validation(response.data);
        });
     },
     loadUsers(){
        axios.get('/Thirdparty/loadUsers').then((data) => {
           this.users = data.data;
        });
     }
  },
  created(){
    this.loadUsers(); 
  }
}

// Option 2 - Adjust the reference
export default{
  data(){
     return {
        users : {}
     }
  },
  methods:{
     addCustomer(){
        var formData = $('#add-customer').serialize();
        axios.post('/Thirdparty', formData).then(function(response){
           helper.validation(response.data);
        });
     },
     loadUsers(){
        let self=this; 
        axios.get('/Thirdparty/loadUsers').then(function(data){
           self.users = data.data;
        });
     }
  },
  created(){
    this.loadUsers(); 
  }
}

Answer 2

When you reference this.users within the callback to axios.get().then() in the function loadUsers(), be mindful that using a standard function instead of an arrow function can cause unexpected behavior. In this case, this does not refer to the Vue instance as intended, leading to scope issues. To resolve this, either switch to an arrow function or adjust the way you reference this:

// Option 1 - Use an arrow function
export default{
  data(){
     return {
        users : {}
     }
  },
  methods:{
     addCustomer(){
        var formData = $('#add-customer').serialize();
        axios.post('/Thirdparty', formData).then((response) => {
           helper.validation(response.data);
        });
     },
     loadUsers(){
        axios.get('/Thirdparty/loadUsers').then((data) => {
           this.users = data.data;
        });
     }
  },
  created(){
    this.loadUsers(); 
  }
}

// Option 2 - Adjust the reference
export default{
  data(){
     return {
        users : {}
     }
  },
  methods:{
     addCustomer(){
        var formData = $('#add-customer').serialize();
        axios.post('/Thirdparty', formData).then(function(response){
           helper.validation(response.data);
        });
     },
     loadUsers(){
        let self=this; 
        axios.get('/Thirdparty/loadUsers').then(function(data){
           self.users = data.data;
        });
     }
  },
  created(){
    this.loadUsers(); 
  }
}

The created function in VueJS may sometimes result in an undefined outcome

Answer №1

Similar questions

My jQuery Ajax seems to have a glitch, can someone help me figure out

When utilizing CKEDITOR, the default TEXTAREA is obscured, and CKEDITOR does not appear

Removing a database record with JQuery

Why is it that the edit or delete button is not functioning when I attempt to click on the next page?

What is the best method to ensure that none of the select option values are left empty?

Is there a way to trigger a Modal to open upon clicking a custom-designed button in MaterialUI?

You are only able to click the button once per day

Flip an image by analyzing the colors beneath it

What is the method to retrieve an object instead of a singular value upon selecting a v-select item?

Error: The 'price' property is undefined and cannot be read at path C:NODEJS-COMPLETE-GUIDEcontrollersshop.js on line 45, character 37

Error: The property 'rows' cannot be read because it is undefined

Exploring the capabilities of NEXTJS for retrieving data from the server

Ways to transition into a developer role

Showing a collection of cards within a dynamic container set up in a 3x3 grid layout to start

Exploring the Dynamic Connection: AngularJS and MongoDB

Discover the Phillips Hue Bridge within the operational web application on a separate network

Issues with the initial drop functionality in jQuery UI

Changing a particular field value within an array of objects in Angular 4

Ways to condense a text by using dots in the middle portion of it

barchart rendered in SVG without the use of any external libraries