JSON.parse. Enable Plotly under Libraries, wait until it is checked, then paste the whole editor.

Goal

Run every block and confirm the chart is visible.

const rows = JSON.parse('[{"city":"Nairobi","units":21},{"city":"Mombasa","units":15}]');
document.body.innerHTML = '<div id="plot" style="width:480px;height:320px"></div>';
Plotly.newPlot("plot", [{ type: "bar", x: rows.map(r => r.city), y: rows.map(r => r.units) }], { title: "JSON" });
console.log(rows.length);

document.body.innerHTML = '<div id="plot" style="width:480px;height:320px"></div>';
Plotly.newPlot("plot", [{ type: "bar", x: ["Nairobi", "Mombasa", "Kisumu", "Nakuru", "Eldoret"], y: [21, 15, 15, 18, 12] }], { title: "Units" });
console.log("bar");

document.body.innerHTML = '<div id="plot" style="width:480px;height:320px"></div>';
Plotly.newPlot("plot", [{ type: "scatter", mode: "lines+markers", x: ["Jan", "Feb", "Mar", "Apr"], y: [48, 55, 92, 150] }], { title: "Rain" });
console.log("line");

console.log('files');