firstComeFirstServe.js

function firstComeFirstServe(takeAwayOrders, eatInOrders, servedOrders) {

  // if any orders are not accounted for, return false
  if ([...takeAwayOrders, ...eatInOrders].length != servedOrders.length) {
    return false
  }

  servedOrders.forEach(order => {
    if (takeAwayOrders[0] === order) {
      // match! 
      takeAwayOrders.shift()
      
    } else if (eatInOrders[0] === order) {
      // match!
      eatInOrders.shift()
      
    } else {
      // no match, not first-come first-serve
      return false
    }
  })
  
  // check for remaining extra orders
  return [...takeAwayOrders, ...eatInOrders].length == 0 ? true : false
}