> For the complete documentation index, see [llms.txt](https://docs.mapbox.com/mapbox-gl-js/llms.txt)
# Update a feature in realtime
This example shows how to change an existing feature on a map by updating its data.
It shows the progression of a path by adding new coordinates to a feature in a [`line` layer](https://docs.mapbox.com/style-spec/reference/layers/#line). This approach is useful for visualizing real-time data sources.
Calling [`setData`](https://docs.mapbox.com/mapbox-gl-js/api/sources/#geojsonsource#setdata) begins a new render cycle which makes the updates appear in real time without explicitly creating an animation. [`panTo`](https://docs.mapbox.com/mapbox-gl-js/api/map/#map#panto) then follows the leading edge of the line to keep it on screen.
> Example code:
**JavaScript**
```html
Update a feature in realtime
```
**React**
```jsx
import React, { useEffect, useRef } from 'react';
import * as mapboxgl from 'mapbox-gl/esm';
import 'mapbox-gl/dist/mapbox-gl.css';
const MapboxExample = () => {
const mapContainerRef = useRef();
const mapRef = useRef();
useEffect(() => {
mapRef.current = new mapboxgl.Map({
// TO MAKE THE MAP APPEAR YOU MUST
// ADD YOUR ACCESS TOKEN FROM
// https://account.mapbox.com
accessToken: 'YOUR_MAPBOX_ACCESS_TOKEN',
container: mapContainerRef.current,
style: 'mapbox://styles/mapbox/standard-satellite',
zoom: 0
});
mapRef.current.on('load', async () => {
const response = await fetch(
'https://docs.mapbox.com/mapbox-gl-js/assets/hike.geojson'
);
const data = await response.json();
const coordinates = data.features[0].geometry.coordinates;
data.features[0].geometry.coordinates = [coordinates[0]];
mapRef.current.addSource('trace', { type: 'geojson', data: data });
mapRef.current.addLayer({
id: 'trace',
type: 'line',
source: 'trace',
paint: {
'line-color': 'yellow',
'line-opacity': 0.75,
'line-width': 5
}
});
mapRef.current.jumpTo({ center: coordinates[0], zoom: 14 });
mapRef.current.setPitch(30);
let i = 0;
const timer = setInterval(() => {
if (i < coordinates.length) {
data.features[0].geometry.coordinates.push(coordinates[i]);
mapRef.current.getSource('trace').setData(data);
mapRef.current.panTo(coordinates[i]);
i++;
} else {
window.clearInterval(timer);
}
}, 10);
});
}, []);
return ;
};
export default MapboxExample;
```