Download YouTube Screenshot by running this in the console

YouTubeScreenshot.js

(() => {
    const youtubeVideoSelector = 'video';

    const video = document.querySelector(youtubeVideoSelector);
    const width = video.videoWidth;
    const height = video.videoHeight;

    const canvas = document.createElement('canvas');
    const context = canvas.getContext('2d');
    canvas.width = width;
    canvas.height = height;

    context.fillRect(0, 0, width, height);
    context.drawImage(video, 0, 0, width, height);

    canvas.toBlob((blob) => {
        const a = document.createElement('a');
        a.href = URL.createObjectURL(blob);

        // Take advantage of known US English format
        const parts = new Intl.DateTimeFormat('en-us', {
            year: 'numeric',
            month: '2-digit',
            day: '2-digit',
        }).formatToParts(new Date());
        a.download = `YouTube-Screenshot_${parts[4].value}-${parts[0].value}-${parts[2].value}`;
        
        a.click();

        setTimeout(() => {
            URL.revokeObjectURL(a.href);
        }, 1000);
    });
})();