Use html2canvas to capture a screenshot of the page upon any errors in the console via window.onerror event and send it to Slack as alert/notification. Image are stored with imgbb.com

error-detection.js

const script = document.createElement('script');
script.type = 'text/javascript';
script.src = '//html2canvas.hertzen.com/dist/html2canvas.min.js';
document.head.appendChild(script);
window.onerror = async function () {
	const { 0: errorMessage, 1: fileName, 2: lineNumber, 3: columnNumber, 4: errorObj } = arguments;
	if (typeof html2canvas === 'function') {
		html2canvas(document.body, { scale: 1.0 }).then(async (canvas) => {
			const base64image = canvas.toDataURL('image/png');
			let imageData = base64image.split('base64,');
			imageData = imageData[1];
			const formData = new FormData();
			formData.append('image', imageData);
			await fetch('https://api.imgbb.com/1/upload?&key=<YOUR_API_KEY>', {
				method: 'POST',
				cache: 'no-cache',
				body: formData,
			}).then(async (response) => {
				const data = await response.json();
				const screenshot = data.data.image.url || '';
				const message = {
					attachments: [
						{
							image_url: screenshot,
							mrkdwn: true,
							fallback: `${errorMessage}`,
							text: `${errorMessage}`,
							author_name: fileName,
							author_link: fileName,
							footer: 'window.onerror Notification',
							ts: new Date().getTime() / 1000,
							fields: [
								{
									title: 'FileName',
									value: fileName,
									short: true,
								},
								{
									title: 'Error Message',
									value: errorMessage,
									short: true,
								},
								{
									title: 'Line Number',
									value: lineNumber,
									short: true,
								},
								{
									title: 'Column Number',
									value: columnNumber,
									short: true,
								},
							],
							color: '#ff0000',
						},
					],
				};
				await fetch('https://hooks.slack.com/services/<YOUR_API_KEY>', {
					method: 'POST',
					cache: 'no-cache',
					body: JSON.stringify(message),
				});
			});
		});
	}
};

message-only-without-screenshot.js

window.onerror = function () {
	const { 0: errorMessage, 1: fileName, 2: lineNumber, 3: columnNumber, 4: errorObj } = arguments;
	const message = {
		attachments: [
			{
				mrkdwn: true,
				fallback: `${errorMessage}`,
				text: `${errorMessage}`,
				author_name: fileName,
				author_link: fileName,
				footer: 'window.onerror Notification',
				ts: new Date().getTime() / 1000,
				fields: [
					{
						title: 'FileName',
						value: fileName,
						short: true,
					},
					{
						title: 'Error Message',
						value: errorMessage,
						short: true,
					},
					{
						title: 'Line Number',
						value: lineNumber,
						short: true,
					},
					{
						title: 'Column Number',
						value: columnNumber,
						short: true,
					},
					{
						title: 'Error Object',
						value: JSON.stringify(errorObj),
					},
				],
				color: '#ff0000',
			},
		],
	};
	fetch('https://hooks.slack.com/services/<YOUR-HOOKS-SECRET>', {
		method: 'POST',
		cache: 'no-cache',
		body: JSON.stringify(message),
	});
};