l = FileInput(accept='.json')

l.js_on_change('value', CustomJS(code="""\
const {Document} = Bokeh.require('document/document');
const data = JSON.parse(atob(cb_obj.value));
const doc = Document.from_json(data);
Bokeh.embed.add_document_standalone(doc, document.getElementById('document-container'), [], true);
cb_obj.disabled = true;
"""))