---
title: "Update a feature in realtime | JavaScript maps SDK"
description: "Change an existing feature on your map in real-time by updating its data."
---
> For AI agents: a documentation index is available at [/llms.txt](https://docs.maptiler.com/llms.txt). Markdown versions of all pages are available by appending .md to any URL.
# Update a feature in realtime
Change an existing feature on your map in real-time by updating its data.
### NPM module setup
```bash
npm install --save @maptiler/sdk
```
#### main.js
```js
import { Map, MapStyle, config } from '@maptiler/sdk';
import '@maptiler/sdk/dist/maptiler-sdk.css';
config.apiKey = 'YOUR_MAPTILER_API_KEY_HERE';
const map = new Map({
container: 'map',
style: MapStyle.OUTDOOR,
zoom: 0
});
map.on('load', function () {
// We use D3 to fetch the JSON here so that we can parse and use it separately
// from GL JS's use in the added source. You can use any request method (library
// or otherwise) that you want.
d3.json(
'https://docs.maptiler.com/sdk-js/assets/hike.geojson',
function (err, data) {
if (err) throw err;
// save full coordinate list for later
const coordinates = data.features[0].geometry.coordinates;
// start by showing just the first coordinate
data.features[0].geometry.coordinates = [coordinates[0]];
// add it to the map
map.addSource('trace', { type: 'geojson', data: data });
map.addLayer({
'id': 'trace',
'type': 'line',
'source': 'trace',
'paint': {
'line-color': 'yellow',
'line-opacity': 0.75,
'line-width': 5
}
});
// setup the viewport
map.jumpTo({ 'center': coordinates[0], 'zoom': 14 });
map.setPitch(30);
// on a regular basis, add more coordinates from the saved list and update the map
let i = 0;
const timer = window.setInterval(function () {
if (i < coordinates.length) {
data.features[0].geometry.coordinates.push(
coordinates[i]
);
map.getSource('trace').setData(data);
map.panTo(coordinates[i]);
i++;
} else {
window.clearInterval(timer);
}
}, 10);
}
);
});
```
#### index.html
```html
Update a feature in realtime | NPM example
```
#### style.css
```css
body {margin: 0; padding: 0;}
#map {position: absolute; top: 0; bottom: 0; width: 100%;}
```
### Basic JavaScript setup
```html
Update a feature in realtime
```
## Related examples
### [Add live realtime data](https://docs.maptiler.com/sdk-js/examples/live-geojson/)
Examples
Use real-time GeoJSON data streams to move a symbol on your map.
### [Animate a point](https://docs.maptiler.com/sdk-js/examples/animate-point-along-line/)
Examples
Animate a point position using GeoJSON frame updates.
### [GeoJSON line layer](https://docs.maptiler.com/sdk-js/examples/geojson-line/)
Tutorials
Add a GeoJSON line overlay to the map application.