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React-redux map error TypeError: Cannot read property ‘map’ of undefined

I get the following error in my ReactJS code:

TypeError: Cannot read property ‘map’ of undefined

This is based on the following code:

import React, { Component } from "react";
import { connect } from "react-redux";
import { ListGroup, ListGroupItem } from "reactstrap";
import { bindActionCreators } from "redux";
import * as categoryActions from "../../redux/actions/categoryActions";

class CategoryList extends Component {
  componentDidMount() {
    this.props.actions.getCategories();
  }
  render() {
    return (
      <div>
        <h3>Categories</h3>
        <ListGroup>
          {this.props.categories.map(category => (
            <ListGroupItem key={category.id}>
              {category.categoryName}
            </ListGroupItem>
          ))}
        </ListGroup>
        <h5>The Category: {this.props.currentCategory.categoryName}</h5>
      </div>
    );
  }
}

function mapStateToProps(state) {
  return {
    currentCategory: state.changeCategoryReducer,
    categories: state.CategoryListReducer,
  };
}

function mapDispatchToProps(dispatch) {
  return {
    actions: {
      getCategories: bindActionCreators(
        categoryActions.getCategories,
        dispatch
      ),
      changeCategory: bindActionCreators(
        categoryActions.getCategories,
        dispatch
      ),
    },
  };
}
export default connect(mapStateToProps)(CategoryList);

I don’t know how can I fix this error. Can you help me please?

Answer

Try the following in your render function

return (
  <div>
    <h3>Categories</h3>
    <ListGroup>
      {this.props.categories && this.props.categories.map(category => (
        <ListGroupItem key={category.id}>
          {category.categoryName}
        </ListGroupItem>
      ))}
    </ListGroup>
    <h5>The Category: {this.props.currentCategory.categoryName}</h5>
  </div>
);