`The 'async' modifier can only be used in TypeScript files.ts(8009)` error when using async in react.js

You can try either

async handleClick(dish) {
  this.props.addOrder(dish)
  localStorage.setItem("order", this.props.order)
  alert(`${dish.name} added to your order!`)
}

OR

handleClick = async(dish) => {
  this.props.addOrder(dish)
  localStorage.setItem("order", this.props.order)
  alert(`${dish.name} added to your order!`)
}