createElementNS

NS => name space

let element = document.createElementNS(namespaceURI, qualifiedName[, options]);

动态创建svg

var svgDom = document.createElementNS('http://www.w3.org/2000/svg','svg');
svgDom.setAttribute('width','1000');
svgDom.setAttribute('height','1000');
document.body.appendChild(svgDom);

另外

document.createElement("div")==document.createElementNS("http://www.w3.org/1999/xhtml","div");