how to update array in object state code example

Example 1: how to update array in react state

this.setState(prevState => ({
  arrayvar: [...prevState.arrayvar, newelement]
}))

Example 2: update object in array state by index

this.setState(({items}) => ({
    items: [
        ...items.slice(0,1),
        {
            ...items[1],
            name: 'newName',
        },
        ...items.slice(2)
    ]
}));