execute the function within the data() method

Question

execute the function within the data() method

I'm currently working on retrieving data for my search tree, and I'm facing issues with fetching the data directly from axios or calling a function because it cannot be found.

export default {
 name: 'SideNavMenu',
 data () {
  return {
      searchValue: '',
      treeData: this.getData(),
      treeOptions: {

        fetchData(node) {
          this.onNodeSelected(node)

        }
      },
  }
},

Within the data() method, I have a section called treeOptions where I am attempting to invoke a function named onNodeSelected. However, an error message is displayed:

"TypeError: this.onNodeSelected is not a function"

Is there anyone who can assist with resolving this issue?

javascript vue.js axios vue-cli

Answer 1

Answer №1

When you utilize the keyword this, you are attempting to access a member of the object currently in use.

In JavaScript, the use of curly braces {} actually creates a new object, requiring either the object to have the onNodeSelected implemented or for a different function to be called that allows for the call on an object with the necessary function implementation.

export default {
    name: 'SideNavMenu',
    data () {
        return {
            searchValue: '',
            treeData: this.getData(), // <--- This
            treeOptions: {

                fetchData(node) {
                    this.onNodeSelected(node) // <--- and this
                }
            },
        }
},

// Calling functions within this object :
{
    searchValue: '',
    treeData: this.getData(),
    treeOptions: {
        fetchData(node) {
            this.onNodeSelected(node)
        }
    },
// Rather than calling functions from the intended object

It's best practice to avoid nesting object blocks within each other as it can lead to code becoming hard to read. Instead, create functions within a single object when necessary.

If you were to try accessing a value from treeData, you would likely encounter a similar error message.

Answer 2

When you utilize the keyword this, you are attempting to access a member of the object currently in use.

In JavaScript, the use of curly braces {} actually creates a new object, requiring either the object to have the onNodeSelected implemented or for a different function to be called that allows for the call on an object with the necessary function implementation.

export default {
    name: 'SideNavMenu',
    data () {
        return {
            searchValue: '',
            treeData: this.getData(), // <--- This
            treeOptions: {

                fetchData(node) {
                    this.onNodeSelected(node) // <--- and this
                }
            },
        }
},

// Calling functions within this object :
{
    searchValue: '',
    treeData: this.getData(),
    treeOptions: {
        fetchData(node) {
            this.onNodeSelected(node)
        }
    },
// Rather than calling functions from the intended object

It's best practice to avoid nesting object blocks within each other as it can lead to code becoming hard to read. Instead, create functions within a single object when necessary.

If you were to try accessing a value from treeData, you would likely encounter a similar error message.

Answer 3

Answer №2

It seems like you are not calling the function or returning anything from it. Maybe you intended to do something like this:

export default {
 name: 'SideNavMenu',
 data () {
  return {
      searchValue: '',
      treeData: this.getData(),
      treeOptions: fetchData(node) {
          return this.onNodeSelected(node)
      },
  }
},

However, it is generally not recommended to include functions inside data properties. A better approach would be to declare your variables with empty values initially, and then populate them when you receive the data in beforeCreate, created, or mounted hooks. Here's an example:

export default {
  name: 'SideNavMenu',
  data () {
    return {
      searchValue: '',
      treeData: [],
      treeOptions: {},
    }
  },
  methods: {
    getData(){
      // fetch data here
    },
    fetchData(node){
       this.onNodeSelected(node).then(options => this.treeOptions = options)
    }
  },
  mounted(){
     this.getData().then(data => this.treeData = data)
  }
},

Alternatively, if you prefer using async/await:

export default {
  name: 'SideNavMenu',
  data () {
    return {
      searchValue: '',
      treeData: [],
      treeOptions: {},
    }
  },
  methods: {
    getData(){
      // fetch data here
    },
    async fetchData(node){
       this.treeOptions = await this.onNodeSelected(node) 
    }
  },
  async mounted(){
     this.treeData = await this.getData()
  }
},

Answer 4

It seems like you are not calling the function or returning anything from it. Maybe you intended to do something like this:

export default {
 name: 'SideNavMenu',
 data () {
  return {
      searchValue: '',
      treeData: this.getData(),
      treeOptions: fetchData(node) {
          return this.onNodeSelected(node)
      },
  }
},

However, it is generally not recommended to include functions inside data properties. A better approach would be to declare your variables with empty values initially, and then populate them when you receive the data in beforeCreate, created, or mounted hooks. Here's an example:

export default {
  name: 'SideNavMenu',
  data () {
    return {
      searchValue: '',
      treeData: [],
      treeOptions: {},
    }
  },
  methods: {
    getData(){
      // fetch data here
    },
    fetchData(node){
       this.onNodeSelected(node).then(options => this.treeOptions = options)
    }
  },
  mounted(){
     this.getData().then(data => this.treeData = data)
  }
},

Alternatively, if you prefer using async/await:

export default {
  name: 'SideNavMenu',
  data () {
    return {
      searchValue: '',
      treeData: [],
      treeOptions: {},
    }
  },
  methods: {
    getData(){
      // fetch data here
    },
    async fetchData(node){
       this.treeOptions = await this.onNodeSelected(node) 
    }
  },
  async mounted(){
     this.treeData = await this.getData()
  }
},

execute the function within the data() method

Answer №1

Answer №2

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