Why is the variable in the dictionary not initialized?

Question

Vue.js

In the data block, I initialize the dictionary

data: () => ({
            filterItem: {
                learning_type: null,
            },
...

however, learning_type remains undefined:

why is that? And how do you set the learning_type key to null instead of undefined ?

Answer 1

¯\_(ツ)_/¯
In general, I decided so far like this:

mounted() {      
      if (this.filterItem.learning_type === undefined) {
                this.filterItem.learning_type = null
       }
}

If there is a better solution, I will mark it as the answer.

Answer 2

data() {
  return {
    filterItem: {
      learning_type: null,
    }
  }
}