range开始节点和结束节点

sc = range.startContainer, so = range.startOffsest

ec = range.endContainer, eo=range.endOffset

 

startNode = (sc.nodeType == 3 || so === 0) ? sc : sc.childNodes[so - 1],

endNode = (ec.nodeType == 3 || eo === 0) ? ec : ec.childNodes[eo - 1];

 

三种情况：文本节点，偏移量为0，偏移量不为0