render-header  this property uses the  render  function of  vue  to create the component. 
 Syntax check this: ide/render-function.html" rel=" nofollow noreferrer "> https://cn.vuejs.org/v2/guide.
  render-header  check out the following example:  http://jsfiddle.net/770tasuc/
 <el-table-column prop="diffTime" label="" width="120" align="center">
    <template slot-scope="scope">
        <el-tooltip :content="scope.row.createTime">
            <div slot>{{scope.row.diffTime}}</div>
        </el-tooltip>
    </template>
</el-table-column>
 
The first parameter of the 
 h function is the tag signature, the second is the object used to set the style, events, attributes, etc., and the third parameter is the array, which is used to set the tag to contain child tags, which can also be rendered with the h function 
.
 renderHeader(h, data) {
        var column = data.column;//data
        var index = data.$index;
        var method = () => {
            this.clickHandler(index);
        };
        return h('span', { //
            style: {
                cursor: 'pointer'//
            },
            on: {
                click: method
            }
        }, [column.label, h('img', {
            style: {
                verticalAlign: 'middle',
                marginLeft: '5px',
                marginTop: '-3px',
                width: '12px'
            },
            domProps: {
                src: this.imgurl[index]
            }
        })]);
    }
    
    <span style="cursor: pointer;">//
     //column.label
    <img src="" style="vertical-align: middle; margin-left: 5px; margin-top: -3px; width:12px;">//
    </span>