Simple implementation of Undo and Redo With State History

StateHistory.js

class StateHistory{
    historyIndex = 0;
    initialState = {num: 1};
    stateHistory = [this.initialState];

    setState(fn){
        this.stateHistory = [...this.stateHistory, fn(this.stateHistory[this.historyIndex])];
        this.historyIndex++;
    }

    get hasUndo(){
      return this.historyIndex > 0;
    }

    get hasRedo(){
      return this.historyIndex < this.stateHistory.length - 1;
    }

    redo(fn) {
        if(this.hasRedo) {
             this.historyIndex++
             fn(this.stateHistory[this.historyIndex]);
        }
    }

    undo(fn){
        if(this.hasUndo) {
             this.historyIndex--;
             fn(this.stateHistory[this.historyIndex]);
        }
    }
}

const state = new StateHistory();

state.setState((curr) => {
    console.log("Current State",curr)
    return {
        num:5
    };
});

state.setState(() => {
    return {
        num:6
    };
});

state.setState(() => {
   return {
        num:7
    };
});


state.undo((prevState) => {
    console.log("prevState:",prevState) // Will be { num:  6 }
})


console.log(state.hasRedo); // Will be true