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

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