calculator.js

var data = {
  currentValue: 0,
  operator: ""
}

const operators = ["+", "-", "x", "/"]

keys.forEach(key =>{ // output 
  key.addEventListener('click', () =>{
    // if not a number and an operator then we can "save" the display value to our data object and get ready to do some math
   if(operators.includes(key.value)){
     //update our data object current value to be the current display
     data.currentValue = display.value
     // then change the display to be the "=" view or other operator etc
     display.value =  key.value;
     // save the operator to our data objet to get ready to use for some math on the next display value
     data.operator = key.value
   } else {
     // other wise we want to keep adding digits: 6  68  684
      display.value =  display.value + key.value;
   }
  })
})