Map function not return item in render reactjs?

Question

here is code, why my map function not return item in div. I have use array of object in state function. Here is my simple code. I have XML data in componentwiillrecieveprops. is there any issue by componentwillmount. I do not understand why map function in map my array of state.

import React from 'react';
import TextField from 'material-ui/TextField';
var self;

export default class NewAuthoring extends React.Component {
    constructor(props) {
        super(props);
        self = this;
        this.state = {
            sampleState : "OriginalState",
            task : [
                {event:"First data",eventpara:"First Data"},
                {event:"Second data",eventpara:"Second Data"},
                {event:"Third data",eventpara:"Third Data"}
            ]
        }
    }

    componentWillReceiveProps(nextProps) {
        console.log(nextProps.xml)
        if(this.props != nextProps) {
            //Do Something when any props recieve
            this.setState({sampleState:nextProps.xml});
        }
    }

    componentWillMount() {
        //Do something before component renders
        let xml ="<div type=”timeline/slideshow”><section><header></header><article></article></section><section><header></header><article></article></section><section><header></header><article></article></section><section><header></header><article></article></section></div>";
        self.props.getChildXml(xml);
    }
    
    componentDidMount() {
        //Do Something when component is mounted

    }

    handleChange(e) {
        //getChildXml function will update the xml with the given 
        //parameter and will also change the xml dialog value
        let xml ="<div type=”timeline/slideshow”><section><header></header><article></article></section><section><header></header><article></article></section><section><header></header><article></article></section><section><header></header><article></article></section></div>";
        self.props.getChildXml(xml);
    }

    render() {
        const myStyle = {
            mainBlock:{
                fontWeight:"bold",
                margin:"2px"
            }
        }
        const div_style = {
            border:'1px solid black',
            margin:10
        }
        {
            this.state.task.map((item,contentIndex) => {
                return (<div>
                    hello
                    {item.event}
                    {item.eventpara} 
                </div>)
            })
        }
    }

}

Any help will be appreciated.

Prakash Sharma · Accepted Answer · 2018-03-02 06:59:28Z

6

You are not returning element from map callback. Also i see that tasks is an array of object, and you are directly rendering object by writting {item}. You need to return the element and should avoid rendering object directly like this

           {
                this.state.task.map((item,contentIndex) => {
                    return (<div>
                        hello
                        {item.event}
                        {item.eventpara} 
                    </div>)
                })
            }

Alternatively you can also avoid use of {} brackets to return the element without writting return keyword.

{
   this.state.task.map((item,contentIndex) => (
     <div>
        hello
        {item.event}
        {item.eventpara} 
     </div>
   ))
}

UPDATE: You need to return something from render function

render() {
        const myStyle = {
            mainBlock:{
                fontWeight:"bold",
                margin:"2px"
            }
        }
        const div_style = {
            border:'1px solid black',
            margin:10
        }

        return (
          <div>
          {
            this.state.task.map((item,contentIndex) => {
                return (<div>
                    hello
                    {item.event}
                    {item.eventpara} 
                </div>)
            })
          }
          </div>
        )
    }

edited Mar 2, 2018 at 6:59

answered Mar 2, 2018 at 6:27

Prakash Sharma

16.7k6 gold badges34 silver badges38 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

stackoverhelp Over a year ago

Uncaught Error: NewAuthoring.render(): A valid React element (or null) must be returned. You may have returned undefined, an array or some other invalid object. >>>>>>> I am getting this error in console

Prakash Sharma Over a year ago

You must return something from render function. Make sure you are returning some element from render function.

stackoverhelp Over a year ago

so i return the hello inside the map function... or what should i do please help if it work then i start my project

Prakash Sharma Over a year ago

Also, the return elements should be a single element. Not an array of element. If possible, update the question with your code.

Miguel Giménez · Accepted Answer · 2018-03-02 08:13:42Z

Since the map pattern is very common in React you could also do something like this:

1: Create a Map/Iterator component

const Iterator = (props) => {
  //you could validate proptypes also...
  if(!props.array.length) return null
  return props.array.map(element => props.component(element))

}

2.return it passing the component as props:

 render() {
        const myStyle = {
            mainBlock:{
                fontWeight:"bold",
                margin:"2px"
            }
        }
        const div_style = {
            border:'1px solid black',
            margin:10
        }
        return <Iterator
                   array={this.state.task}
                   component={ 
                   item=>(<div key={item.event}>hello{item.event} 
                   {item.eventpara} } </div>                           
                />              
      }

Amanshu Kataria · Accepted Answer · 2018-03-02 08:23:24Z

0

Because you're returning nothing in render(). Use it as follows:

render(){
    return(
        {this.state.task.map((item,contentIndex) => {
                return <SomeElement />;
         }
    );
}

answered Mar 2, 2018 at 8:23

Amanshu Kataria

3,4467 gold badges28 silver badges39 bronze badges

Collectives™ on Stack Overflow

Map function not return item in render reactjs?

3 Answers 3

4 Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

4 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related