How to concatenate JSX elements into an array?

Your solution should look like this:

processItems(itemArray) {
    // Create an empty array that will hold the final JSX output.
    let buffer = []

    buffer.push(<div>A</div>);
    buffer.push(<div>B</div>);
    buffer.push(<div>C</div>);


    // And return the buffer for display inside the render() function
    return (
        <div className"container flex center">
            {buffer}
        </div>
    );
}

JSX is not HTML and you cannot assemble the html elements in multiple steps.