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JavaScript React by Example Building the Application Connecting the Confirm Guests Handler

Jonas Wu
Jonas Wu
13,928 Points

props.toggleConfirmationAt is not a function?

Hello all,

I think that I follow all the steps in this video. But after clicking the checkbox. I will get this type error.

How would you recommend to fix this issue? Thank you! :)

in the app.js:

toggleConfirmationAT = (indexToChange) =>
      guests: this.state.guests.map((guest, index) => {
        if (index === indexToChange) {
          return {
            isConfirmed: !guest.isConfirmed
        return guest;


in the GuestList.js:

const GuestList = (props) => {
  return (
      {props.guests.map((guest, index) => (
          handleConfirmation={() => props.toggleConfirmationAt(index)}

GuestList.propTypes = {
  guests: PropTypes.array.isRequired,
  toggleConfirmationAt: PropTypes.func.isRequired

in Guest.js:

const Guest = (props) => {
  return (

Guest.propTypes = {
  name: PropTypes.string.isRequired,
  isConfirmed: PropTypes.bool.isRequired,
  handleConfirmation: PropTypes.func.isRequired

2 Answers

Michael Hulet
Michael Hulet
47,909 Points

I haven't run this to check, but it seems like you'd get an error like this because you're looking for a function named toggleConfirmationAt, but you've previously named it toggleConfirmationAT (notice the capital "T" instead of the lowercase). JavaScript is case-sensitive, which means toggleConfirmationAt is totally different from toggleConfirmationAT. If you make all your Ts lowercase, I think you might have better results 🙂

Jonas Wu
Jonas Wu
13,928 Points

Thank you Michael :)

It works now, I'll be more careful of the cases next time!