element ui table sort 首字母排序

<el-table-column label="文件名" sortable :sort-method="sortByDate" :resizable="true" :show-overflow-tooltip="true" prop="fullPath" min-width="360">
<template slot-scope="scope">
{{scope.row.fullPath}}
</template>
</el-table-column>

sortByDate(obj1, obj2) {
let val1 = obj1.fullPath.substring(0,1);
let val2 = obj2.fullPath.substring(0,1);
return val1.localeCompare(val2)
}