未定义地图React JS

Question

I have a problem maping the component state. I have this export:

export default[
  {
    'menu': 'Usuarios',
    'url' : '',
    'items':[
      {
        'title': 'Nuevo usuario',
        'destino' : '/DashBoard'
      },
      {
        'title': 'Actualizar datos',
        'destino' : '/DashBoard'
      }
    ]

  },
  {
    'menu': 'Socios',
    'url' : '',
    'items':[
      {
        'title': 'Membrecias',
        'destino' : '/DashBoard'
      }
    ]

  },
  {
    'menu': 'Clases',
    'url' : '',
    'items':[
      {
        'title': 'Nuevo usuario',
        'destino' : '/DashBoard'
      }
    ]

  },
  {
    'menu': 'Productos',
    'url' : '',
    'items':[
      {
        'title': 'Nuevo usuario',
        'destino' : '/DashBoard'
      }
    ]

  },
  {
    'menu': 'Compras',
    'url' : '',
    'items':[
      {
        'title': 'Nuevo usuario',
        'destino' : '/DashBoard'
      }
    ]

  },
  {
    'menu': 'Ventas',
    'url' : '',
    'items':[
      {
        'title': 'Nuevo usuario',
        'destino' : '/DashBoard'
      }
    ]

  },
  {
    'menu': 'Estadisticas',
    'url':'/Dashboard'
  },
  {
    'menu': 'Reportes',
    'url': '/DashBoard'
  }
]

The menu routes is not defined so assign '/ DashBoard' to all but it is not a problem.

I have the problem when I try to map the state of the component in the following way:

// Dependencies
import React, {Component} from 'react';
//Data
import mdata from '../../Data/Settings/MenuDash';

class DropTownMenu extends Component{
  constructor(){
    super();
    this.state={
      data: mdata,
    }
  }
  render(){

    return(
      <div className='DropTownMenu'>
        {this.state.data.map((todo,i) =>
          <div key={i}>
          <span>{todo.menu}</span>
          <span>{todo.url}</span>
          <span>{todo.items.map((todo, i)=><span key={i}>{todo.title}</span>)}</span>
      </div>

      )}

      </div>
    );
  }
}
export default DropTownMenu;

Use the 'span' tag just to test this I have to implement it as a list, but I'll take care of that. the question is that this does not give me errors in console but if in the browser, those errors are the following:

Answer 1

In your data array, some of the objects don't have an 'items' array property (last 2).

  {
    'menu': 'Ventas',
    'url' : '',
    //has items
    'items':[
      {
        'title': 'Nuevo usuario',
        'destino' : '/DashBoard'
      }
    ]

  },
  // no items
  {
    'menu': 'Estadisticas',
    'url':'/Dashboard'
  },
  {
    'menu': 'Reportes',
    'url': '/DashBoard'
  }

You can either put in an undefined check or modify the original data so that all objects in the array has an 'items' property.

<span>{Array.isArray(todo.items) && todo.items.map(item => ...)}</span>

Note that the error is saying that it cannot 'read property map of undefined', and it points to 'todo.items.map'. It means 'todo.items' is undefined; not that 'map' doesn't exist on 'todo.items' (technically true, but doesn't pinpoint the problem directly).