How to upload and read CSV files in React.js?

Figured it out. A combination of react-file-reader and HTML5’s FileReader (see this page).

Placed the react-file-reader bit inside of render:

<ReactFileReader handleFiles={this.handleFiles} fileTypes={'.csv'}>
    <button className="btn">Upload</button>
</ReactFileReader>

And then this above.

handleFiles = files => {
    var reader = new FileReader();
    reader.onload = function(e) {
        // Use reader.result
        alert(reader.result)
    }
    reader.readAsText(files[0]);
}