怎么给这img标签赋值

Question

诸如这样用原生js方法

<img src="" alt="">转成这样<img src="" alt="" jroll-viewer-image>

Answer 1

var b = document.getElementsByTagName("img");
b.setAttribute("name","value");

Answer 2

var b = document.querySelector("img"); 
b.setAttribute("jroll-viewer-image", "");