element-plus/docs/examples/table/custom-index.vue

<template>
  <el-table :data="tableData" style="width: 100%">
    <el-table-column type="index" :index="indexMethod" />
    <el-table-column prop="date" label="Date" width="180" />
    <el-table-column prop="name" label="Name" width="180" />
    <el-table-column prop="address" label="Address" />
  </el-table>
</template>

<script lang="ts">
export default {
  data() {
    return {
      tableData: [
        {
          date: '2016-05-03',
          name: 'Tom',
          state: 'California',
          city: 'Los Angeles',
          address: 'No. 189, Grove St, Los Angeles',
          zip: 'CA 90036',
          tag: 'Home',
        },
        {
          date: '2016-05-02',
          name: 'Tom',
          state: 'California',
          city: 'Los Angeles',
          address: 'No. 189, Grove St, Los Angeles',
          zip: 'CA 90036',
          tag: 'Office',
        },
        {
          date: '2016-05-04',
          name: 'Tom',
          state: 'California',
          city: 'Los Angeles',
          address: 'No. 189, Grove St, Los Angeles',
          zip: 'CA 90036',
          tag: 'Home',
        },
        {
          date: '2016-05-01',
          name: 'Tom',
          state: 'California',
          city: 'Los Angeles',
          address: 'No. 189, Grove St, Los Angeles',
          zip: 'CA 90036',
          tag: 'Office',
        },
      ],
    }
  },
  methods: {
    indexMethod(index) {
      return index * 2
    },
  },
}
</script>