[Vuejs]-Accessing "this" in a javascript forEach function

Many built-ins, including forEach include an optional ‘this’ binder:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach

use that to your advantage:

this.inputList.forEach(function (element) {
   predictionParams[element.detail] = this.form[element.detail]
},this)

supported since ie9

arrow function syntax avoids rebinding this

 this.inputList.forEach(element => {
   predictionParams[element.detail] = this.form[element.detail]
 })

You can use Arrow function https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions
It will binding this into the function

 data () {
    return {
      question: [],
      inputList: [],
      form: {}
    }
  },
 methods: {
   onSubmit: () => {
     let predictionParams = {}

     this.inputList.forEach((element) => {
       predictionParams[element.detail] = this.form[element.detail]
     })
   }