Invariant Violation: Objects are not valid as a React child

Question

In my component's render function I have:

render() {     const items = ['EN', 'IT', 'FR', 'GR', 'RU'].map((item) => {       return (<li onClick={this.onItemClick.bind(this, item)} key={item}>{item}</li>);     });     return (       <div>         ...                 <ul>                   {items}                 </ul>          ...       </div>     );   } 

everything renders fine, however when clicking the <li> element I receive the following error:

Uncaught Error: Invariant Violation: Objects are not valid as a React child (found: object with keys {dispatchConfig, dispatchMarker, nativeEvent, target, currentTarget, type, eventPhase, bubbles, cancelable, timeStamp, defaultPrevented, isTrusted, view, detail, screenX, screenY, clientX, clientY, ctrlKey, shiftKey, altKey, metaKey, getModifierState, button, buttons, relatedTarget, pageX, pageY, isDefaultPrevented, isPropagationStopped, _dispatchListeners, _dispatchIDs}). If you meant to render a collection of children, use an array instead or wrap the object using createFragment(object) from the React add-ons. Check the render method of Welcome.

If I change to this.onItemClick.bind(this, item) to (e) => onItemClick(e, item) inside the map function everything works as expected.

If someone could explain what I am doing wrong and explain why do I get this error, would be great

UPDATE 1:
onItemClick function is as follows and removing this.setState results in error disappearing.

onItemClick(e, item) {     this.setState({       lang: item,     }); } 

But I cannot remove this line as I need to update state of this component

Answer 1

I was having this error and it turned out to be that I was unintentionally including an Object in my JSX code that I had expected to be a string value:

return (     <BreadcrumbItem href={routeString}>         {breadcrumbElement}     </BreadcrumbItem> ) 

breadcrumbElement used to be a string but due to a refactor had become an Object. Unfortunately, React's error message didn't do a good job in pointing me to the line where the problem existed. I had to follow my stack trace all the way back up until I recognized the "props" being passed into a component and then I found the offending code.

You'll need to either reference a property of the object that is a string value or convert the Object to a string representation that is desirable. One option might be JSON.stringify if you actually want to see the contents of the Object.

Answer 2

So I got this error when trying to display the createdAt property which is a Date object. If you concatenate .toString() on the end like this, it will do the conversion and eliminate the error. Just posting this as a possible answer in case anyone else ran into the same problem:

{this.props.task.createdAt.toString()}