how to build innerHtml in javascript code example

Example 1: .innerhtml

// .innerHTML method is used to change the html contents of a DOM object
document.getElementById("demo").innerHTML = "Paragraph changed!";

Example 2: javascript create node from innerhtml

function createElement( str ) {
    var frag = document.createDocumentFragment();

    var elem = document.createElement('div');
    elem.innerHTML = str;

    while (elem.childNodes[0]) {
        frag.appendChild(elem.childNodes[0]);
    }
    return frag;
}