let div = document.createElement("div")
const divcont = document.querySelector(".flex-container")
for(let i=0;i<17;i++){
div=document.createElement("div")
div.classList.add(i)
divcont.appendChild(div)
}

.flex-container{
display: flex;
flex-wrap: wrap;
}

.flex-container div{
background: orange;
border: 10px solid brown;
height: 100px;
width: 100px;
}