Edit in JSFiddle

//backtick quotes
//process function
var str1 = "1 + 2 =";

function sum(a, b) {
	return a+b;
}

str1 = `${str1} ${sum(1,2)}`;

document.getElementById("result").innerText = str1;

<h1>String</h1>

<h2>Backtick quotes</h2>

<ul>
<li>to process function</li>
</ul>

<blockquote>
var str1 = `1 + 2 = ${sum(1,2)}`;<br />
result:<br />
<span id="result"></span>
</blockquote>