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index.md
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---
title: "XRInputSourceArray: length property"
short-title: length
slug: Web/API/XRInputSourceArray/length
page-type: web-api-instance-property
status:
- experimental
browser-compat: api.XRInputSourceArray.length
---
{{APIRef("WebXR Device API")}}{{SeeCompatTable}}{{SecureContext_Header}}
The read-only **`length`** property returns an integer value
indicating the number of items in the input source list represented by
the {{domxref("XRInputSourceArray")}} object.
## Value
An integer value indicating the number of {{domxref("XRInputSource")}} objects
representing WebXR input sources are included in the array.
## Examples
In this example, a game that requires at least one input source
uses `length` to check this before proceeding to allow the user to play the
game.
```js
let sources = xrSession.inputSources;
if (sources.length === 0) {
showAlertDialog(
"You need to have at least one controller to play Super Duper Shark Jump Fest 9000.",
[
{ label: "Shop Now", url: "https://www.example.com/shop/controllers" },
{ label: "Quit", handler: quitGame },
],
);
}
```
Here, if `length` is 0, a
hypothetical `showAlertDialog()` function is called with a prompt string
explaining the need for a controller, and an array of objects, each describing a button
and what should happen when it's clicked. The first takes the user to an Amazon.com
search for VR controllers, and the second calls a `quitGame()` function to
start shutting the game program down.
## Specifications
{{Specifications}}
## Browser compatibility
{{Compat}}