React: setting array object in setState

Question

I am trying to reset an array using the setState method in React. In the constructor I have set tile_arrays to null initially.

The first console.log() produces the desired array of N Tile objects after the nested for loops finish. When setState is called and the subsuquent console.log() after, the state is still null and was not updated.

I am not trying to append new information to the states array, but replace it entirely.

createTileArray(){
        let new_array= [];
        let size = this.state.size;
        for(let row = 0; row < size; row++){
            
            for(let column = 0; column < size; column++){
                
                if(row === 0 || row === 1){
                    //Player 1
                    new_array.push(new Tile(column, row, true, 1))
                }
                else if(row === size - 1 || row === size - 2){
                    //Player 2
                    new_array.push(new Tile(column, row, true, 2))
                }
                else{
                    //Empty Tile
                    new_array.push(new Tile(column, row, false, 0))
                }

            }
        }
        console.log("Tile to be set into the state", new_array)
        this.setState({
            tile_arrays:new_array
            
        },
        () => console.log("Updated Tiles: ", this.state.tile_arrays))
    }

Answer 1

setState is asynchronous, but it does allow a callback.

 this.setState(
   { tile_arrays: tile_array },
   () => console.log("Updated Tiles: ", this.state.tile_arrays)
 )
    

Answer 2

Copied and pasted your code in a snippet to demonstrate the comment I made one hour ago.

Try logging it in render

 class Tile { constructor(column, row, something, player) { this.column = column; this.row = row; this.something = something; this.player = player; } } class App extends React.Component { state = { size: 3, }; createTileArray() { let new_array = []; let size = this.state.size; for (let row = 0; row < size; row++) { for (let column = 0; column < size; column++) { if (row === 0 || row === 1) { //Player 1 new_array.push(new Tile(column, row, true, 1)); } else if (row === size - 1 || row === size - 2) { //Player 2 new_array.push(new Tile(column, row, true, 2)); } else { //Empty Tile new_array.push(new Tile(column, row, false, 0)); } } } console.log('Tile to be set into the state', new_array); this.setState({ tile_arrays: new_array, }); } componentDidMount() { this.createTileArray(); } render() { //was that so difficult? console.log('tile arrays', this.state.tile_arrays); return ( <pre>{JSON.stringify(this.state, undefined, 2)}</pre> ); } } ReactDOM.render(<App />, document.getElementById('root'));

 <script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.4/umd/react.production.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.4/umd/react-dom.production.min.js"></script> <div id="root"></div>

Answer 3

After a little testing, I have found a solution. In my initial constructor for the component, instead of setting

tile_arrays:null

I set it to equal an empty array

tile_arrays:[]

The problem seems to be fixed and working now.