Edit in JSFiddle

function demo() {
	document.getElementById('redditUrlInput').value = 'https://www.reddit.com/r/food/comments/60jxzo/homemade_breakfast_sugar_cookies/';
	auto();
}
function auto() {
	const url = document.getElementById('redditUrlInput').value;
	generateEmbed(url);
}
function generateEmbed(url) {
	const regPatt = /reddit\.com\/r\/[^\/]+\/comments\/([^\/]{6,})\//;
	if (regPatt.test(url)) {
		const fullname = 't3_' + regPatt.exec(url)[1];
		fetch(`https://api.reddit.com/api/info/?id=${fullname}`)
			.then(res => res.json())
			.then(json => generateEmbedFromRedditJson(json));
	}
	else {
		alert('Please enter a valid reddit post URL.')
	}
}

/**
 * Parse and generate embed from API response
 * @param {Object} redditJson 
 */
function generateEmbedFromRedditJson(redditJson) {
	console.log(redditJson);
	const selfData = redditJson.data.children[0].data;
	const { author, permalink, score, thumbnail, title, url } = selfData;
	const subreddit = selfData.subreddit_name_prefixed;
	const html = `
	<div class="reddit-embed">
		<div class="header">
			<div class="poster">Posted by ${author}</div>
			<div class="title"><a href="${permalink}" target="_blank">${title}</a></div>
		</div>
		<div class="body-left">
			<div class="imageWrapper">
				<img src="${thumbnail}" />
			</div>
		</div>
		<div class="body-right">
			<div class="score">${String.fromCharCode(0x2195)} = ${score}</div>
		</div>
	</div>
	`;
	document.getElementById('embedTarget').innerHTML = html;
}
<!-- UI -->
<div class="top">
	<input type="url" id="redditUrlInput" placeholder="https://www.reddit.com/r/food/comments/60jxzo/homemade_breakfast_sugar_cookies/" />
	<button onclick="auto()">Generate</button>
	<button onclick="demo()">Demo</button>
</div>
<div id="embedTarget">
</div>
.top {
	width: 100%;
	margin-bottom: 10px;
}
#redditUrlInput {
	width: 50%;
	display: inline-block;
	max-width: 400px;
	margin-right: 10px;
	margin-bottom: 10px;
}
button {
	width: calc(20% - 20px);
	min-width: 80px;
	display: inline-block;
}

.reddit-embed {
	width: 350px;
	height: 200px;
	border: 4px solid black;
	box-shadow: 5px 5px 5px 0px #000000;
}

.poster {
	color: grey;
}

.title, .title a {
	color: black !important;
	font-weight: bolder;
	text-align: center;
	padding: 8px;
}

.reddit-embed {
	padding-left: 4px;
}

.body-left {
	width: 80%;
}

.body-right {
	width: 25%;
	margin-left: 75%;
	padding-top: 10px;
}

.body-left {
	float: left;
}
.imageWrapper {
	width: 100%;
	text-align: center;
	padding: 6px;
}

.imageWrapper img {
	height: 131px;
	width: auto;
	border-radius: 10px;
}