Edit in JSFiddle

hello = document.querySelector("#divHello");
flgW = false;
say();
function say()
{
    if(flgW) {
        hello.innerHTML = 'Ho!';
    }
    else {
        hello.innerHTML = 'Hi!';
    }        
    flgW = !flgW;
    setTimeout(say, 1000);
}

<div id="divHello">
</div>

#divHello {
    background: black;
    color: white;
    border-radius: 10px;
    width: 100px;
    height: 100px;
    margin: auto;
    text-align: center;
    display: table-cell;
    vertical-align: middle;        
    font-size: 40px;
}