How can I use JavaScript on the client side to detect if the page was encrypted?

Is it possible to detect, on the client side, whether the user is using an encrypted page or not?

Put another way -- I want to know if the URL of the current page starts with http or https.

Use window.location.protocol to check if it is https:

function isSecure()
{
   return window.location.protocol == 'https:';
}

Alternatively you can omit specifying "window" if you don't have a locally scoped location.

function isSecure()
{
   return location.protocol == 'https:';
}

As google analytics taught me:

if ("https:" == document.location.protocol) {
    /* secure */
} else {
    /* unsecure */
}

Second method for newest browsers:

var secure = window.isSecureContext;

or just get isSecureContext:

if (isSecureContext) {
   ...
}

More here: https://developer.mozilla.org/en-US/docs/Web/Security/Secure_Contexts#Feature_detection#Feature_detection

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