Use the screen.colorDepth property in JavaScript to return a number of bits used to display a color on the window screen.
Example
You can try to run the following code to return the screen color depth in JavaScript.
<!DOCTYPE html>
<html>
<body>
<script>
document.write("Screen width: " + screen.width);
document.write("<br>Screen height: " + screen.height);
document.write("<br>Color Depth: " + screen.colorDepth);
</script>
</body>
</html>