How do i set a draggable attribute for my list element using javascript? [duplicate]

I want to set the draggable attribute of my list item to be true every time the button is clicked but theres an error.

const startDrag = function(){
    const li = document.getElementsByClassName('newLi')
    li.setAttribute('draggable', "true");
    startDraggable();
}

Error

TypeError: li.setAttribute is not a function