JSFiddle - React, Tailwind, and code Playground

JavaScript

var workshops = [
  {
    name: 'apples',
    WorkshopId: '19'
  },
  {
    name: 'oranges',
    WorkshopId: '3b'
  },
  {
    name: 'pears',
    WorkshopId: 'x6'
  },
  {
    name: 'pineapples',
    WorkshopId: '55'
  },
  {
    name: 'watermelons',
    WorkshopId: '8v'
  }
];

var selectedWorkshops = [
  {
    name: 'oranges',
    WorkshopId: '3b'
  },
  {
    name: 'watermelons',
    WorkshopId: '8v'
  },
  {
    name: 'pears',
    WorkshopId: 'x6'
  }
];

var registeredWorkshops = [];
var flipWorkshops = function(){
    var numberOfWorkshops = selectedWorkshops.length;
    var X = 1;
    for(var i = 0; i < numberOfWorkshops; i++ ){
        registeredWorkshops.push(selectedWorkshops[i]);
        for(var j = 0, arrayLength = workshops.length; j < arrayLength; j++) {
            var selectedWorkshop = selectedWorkshops[i];
            var originalWorkshop = workshops[j];
            if(selectedWorkshop == originalWorkshop){
                var matchingWorkshop = j;
                workshops.splice(j, 1);
                selectedWorkshops.splice(i, 1);
            }
        }
    }
};
flipWorkshops();
console.log(workshops);
console.log(selectedWorkshops);
console.log(registeredWorkshops);