Uncaught TypeError: Cannot set property 'innerHTML' of null [VueJs]

Question

I see previous questions about the same problem faced me, but I try to solve it based on the solution of the questions! but it does not work

In my <template> :

<modal name="MyModal" >
  <span class="myClass" id="visible">visible</span>
</modal>

In my <script> :

export default {
name: "myProject",
data: function() {
 return {}
},
methods:
 Open_EditTask: function() {

  this.$modal.show("MyModal");

  this.CurrentTask = this.MyTask;

  if ( app.EditTask.visible == true ) { document.getElementById('visible').innerHTML = 'visible'; }
  else { document.getElementById('visible').innerHTML = 'hidden'; }
 }
} 

I used modal plugin to create the modal.

My problem is when the modal opened .. the text not changed based on the app.EditTask.variable value, but when I try to print the value of it .. it shows me the value of it either true or false.

Error message:

Uncaught TypeError: Cannot set property 'innerHTML' of null

Answer 1

Why do you not use computed, it's very easy.

Template:

<modal name="MyModal" >
  <span class="myClass" id="visible"> {{ isVisible }} </span>
</modal>

Javascript:

export default {
  name: "myProject",
  data: function() {
    return {}
  },
  methods:{
    Open_EditTask: function() {
      ..
    }
  },
  computed: {
    isVisible(){
      return app.EditTask.visible ? 'visible' : 'hidden';
    }
  }
} 

To change class name:

Template:

<modal name="MyModal" >
  <span :class="{myClass: true, hidden: !isVisible, visible: isVisible}" id="visible"></span>
</modal>

Javascript:

export default {
  name: "myProject",
  data: function() {
    return {}
  },
  methods:{
    Open_EditTask: function() {
      ..
    }
  },
  computed: {
    isVisible(){
      return app.EditTask.visible;
    }
  }
}