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JavaScript React by Example Building the Application Writing a Handler to Confirm Guests

Why I have an error on the property map?

When I click on the checkbox the app brokes and generate an error on the property Map.

TypeError: Cannot read property 'map' of undefined App._this.toggleGuestPropertyAt src/App.js:29 26 | 27 | toggleGuestPropertyAt = (property, indexToChange) => 28 | this.setState({

29 | guests: this.state.guests.map((guest, index) => { 30 | if(index === indexToChange){ 31 | return{ 32 | isConfirmed: !guest.isConfirmed,