chart/jsonUpload.js

var inputElement = document.getElementById('jsonfile');
inputElement.addEventListener('change',handleFiles,false);
function handleFiles(){
    let selectedFile = document.getElementById('jsonfile');

    let reader = new FileReader();
    reader.readAsText(selectedFile);

    reader.onload = function(){
        let json = JSON.parse(this.result);
        console.log(json.name);
        console.log(json.age);
    }
}