react class component append to state array code example

Example 1: how to add array data on state react

this.setState({ myArray: [...this.state.myArray, 'new value'] }) //simple value
this.setState({ myArray: [...this.state.myArray, ...[1,2,3] ] }) //another array

Example 2: react how to update state array

const initialState = [
    { name: "foo", counter: 0 },
    { name: "far", counter: 0 },
    { name: "faz", counter: 0 }
  ];

const [state, setState] = useState(initialState);

const clickButton = () => {
	// 1. Make a shallow copy of the array
	let temp_state = [...state];
	
	// 2. Make a shallow copy of the element you want to mutate
	let temp_element = { ...temp_state[0] };
	
	// 3. Update the property you're interested in
	temp_element.counter = temp_element.counter+1;
	
	// 4. Put it back into our array. N.B. we *are* mutating the array here, but that's why we made a copy first
	temp_state[0] = temp_element;
	
	// 5. Set the state to our new copy
	setState( temp_state );
}