Sometimes, we want to fix the ‘Cannot Read Property ‘map’ of Undefined’ error in a React component.
In this article, we’ll look at how to fix the ‘Cannot Read Property ‘map’ of Undefined’ error in a React component.
Fix the ‘Cannot Read Property ‘map’ of Undefined’ Error in a React Component
We may get this if we try to call map on something that doesn’t have a map method.
This may happen to something that we expect to be an array, but it’s not.
Therefore, we should check if the value we’re calling map on is an array before doing anything.
For instance, we can do that by writing:
if (Array.isArray(this.props.data)) {
const commentNodes = this.props.data.map((comment) => {
return (
<div>
<h1>{comment.title}</h1>
</div>
);
});
}
We called Array.isArray to check if this.props.data is an array.
If it is, then we call map to map the data prop to h1 elements.
Conclusion
We may get the ‘Cannot Read Property ‘map’ of Undefined’ error if we try to call map on something that doesn’t have a map method.
This may happen to something that we expect to be an array, but it’s not.
Therefore, we should check if the value we’re calling map on is an array before doing anything.
