获取光标，并且移动至最后

1. 准备一个元素

<div  id="sendMessageInput" contenteditable="true"  spellcheck="false"></div>

1. 调用获取光标方法，传入元素

 this.keepLastIndex(document.getElementById('sendMessageInput'))

keepLastIndex(obj) {
  if (window.getSelection) {
    //ie11 10 9 ff safari
    obj.focus() //解决ff不获取焦点无法定位问题
    var range = window.getSelection() //创建range
    range.selectAllChildren(obj) //range 选择obj下所有子内容
    range.collapseToEnd() //光标移至最后
  } else if (document.selection) {
    //ie10 9 8 7 6 5
    var range = document.selection.createRange() //创建选择对象
    //var range = document.body.createTextRange();
    range.moveToElementText(obj) //range定位到obj
    range.collapse(false) //光标移至最后
    range.select()
  }
},