The MediaTrackSupportedConstraints dictionary's facingMode property is a read-only Boolean value which is present (and set to true) in the object returned by MediaDevices.getSupportedConstraints() if and only if the user agent supports the facingMode constraint. If the constraint isn't supported, it's not included in the list, so this value will never be false.
You can access the supported constraints dictionary by calling navigator.mediaDevices.getSupportedConstraints().
This property is present in the dictionary (and its value is always true) if the user agent supports the facingMode constraint. If the property isn't present, this property is missing from the supported constraints dictionary, and you'll get undefined if you try to look at its value.
js
const result = document.getElementById("result"); const supported = navigator.mediaDevices.getSupportedConstraints().facingMode; result.textContent = supported ? "Supported!" : "Not supported!";
| Desktop | Mobile | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
facingMode |
52 | ≤79 | 42 | No | 39 | 11 | 52 | 52 | 42 | 41 | 11 | 6.0 |
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https://developer.mozilla.org/en-US/docs/Web/API/MediaTrackSupportedConstraints/facingMode