Getting the iPhone X safe area using JavaScript

From https://benfrain.com/how-to-get-the-value-of-phone-notches-environment-variables-env-in-javascript-from-css/. You can find more context in the link.

Within CSS

:root {
    --sat: env(safe-area-inset-top);
    --sar: env(safe-area-inset-right);
    --sab: env(safe-area-inset-bottom);
    --sal: env(safe-area-inset-left);
}

Within JS

getComputedStyle(document.documentElement).getPropertyValue("--sat")