forceToShareEntireScreen.js

async startScreenCapture() {
    let captureMediaStream = null;
    let screen_constraints = {
        video: {
            cursor: "always",
            displaySurface: "monitor"
        }
    };

    try {
        captureMediaStream = await navigator.mediaDevices.getDisplayMedia(screen_constraints);
        let displaySurface = captureMediaStream.getVideoTracks()[0].getSettings().displaySurface;

        if (displaySurface === "monitor") {
            // This means User has not shared his Entire Screen
            // Take the appropriate action needed, like 
            alert(`Please share your entire screen.`);
            return;
        }

    } catch (err) {
        console.log(err.message, err.code);
    }
    return captureMediaStream;
}