JAVASCRIPT

add object to array setstate

 this.setState( prevState => ({
     userFavorites: [...prevState.userFavourites,  {id: 3, title: 'C'}]
 }));

add object in array state react

const handleAdd = (todo) => {
  const newTodos = [...todos];
  newTodos.push(todo);
  setTodos(newTodos);
}

add object in array state react

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

add object to array setstate

To push to the beginning of the array do it this way

   this.setState( prevState => ({
     userFavorites: [{id: 3, title: 'C'}, ...prevState.userFavourites]
  }));

add array of object to state react

var joined = this.state.myArray.concat('new value');
this.setState({ myArray: joined })