JSFiddle - React, Tailwind, and code Playground

HTML

<input type=file id="fileInput" />

JavaScript

document.querySelector('#fileInput').addEventListener('change', handleFile,false)

function handleFile(e){
    var reader = new FileReader;
    var file   = e.target.files[0]

    reader.onload = function(e){
        csv = e.target.result
    }
    
    reader.readAsText(file);
}