updating a array in react state not working

I want to implement a simple undo/redo functionality in a react app. For that, I am trying to keep track of the state.

react state:

  state = {
        schedule : [],
        loads:[],
        undo:[],
        redo:[]
    };

But when I try to update undo[], it always prints an empty array in the first trigger, starts adding items from the second time on wards. Trying to find out why it doesn't update undo[] array in the first go.

const redoUndoObj ={
             oldStateSchedule : this.state.schedule,
             oldStateLoads : this.state.loads
        }


        this.setState({ undo : this.state.undo.concat(redoUndoObj)});

        console.log(this.state.undo);//print [] at first run