document.getElementById("myElement"
.innerHTML = "<p>Hello, World!</p>";
Если нужен хардкор, то так;
Insert HTML with createDocumentFragment
var fragment = document.createDocumentFragment();
var div = document.createElement('div');
div.innerHTML = `
Hello, World!
HTML code.
Item 1
Item 2
Item 3
`;
fragment.appendChild(div);
var container = document.getElementById('container');
container.appendChild(fragment);