Iview multi-header can be implemented in demo, but what's the problem if it can't be implemented in the project?

I want to implement table multiple headers, similar to the effect of
clipboard.png
, but I can"t do it according to the iview demo code. I don"t know what the problem is.

Mar.31,2021

< H1 > header grouping < / H1 >

set children, to column to render the grouping header.

</Table>
</template>
<script>
    export default {
        data () {
            return {
                columns11: [
                    {
                        title: 'Name',
                        key: 'name',
                        align: 'center',
                        width: 200,
                        fixed: 'left',
                        filters: [
                            {
                                label: 'Joe',
                                value: 1
                            },
                            {
                                label: 'John',
                                value: 2
                            }
                        ],
                        filterMultiple: false,
                        filterMethod (value, row) {
                            if (value === 1) {
                                return row.name === 'Joe';
                            } else if (value === 2) {
                                return row.name === 'John Brown';
                            }
                        }
                    },
                    {
                        title: 'Other',
                        align: 'center',
                        children: [
                            {
                                title: 'Age',
                                key: 'age',
                                align: 'center',
                                width: 200,
                                sortable: true
                            },
                            {
                                title: 'Address',
                                align: 'center',
                                children: [
                                    {
                                        title: 'Street',
                                        key: 'street',
                                        align: 'center',
                                        width: 200
                                    },
                                    {
                                        title: 'Block',
                                        align: 'center',
                                        children: [
                                            {
                                                title: 'Building',
                                                key: 'building',
                                                align: 'center',
                                                width: 200,
                                                sortable: true
                                            },
                                            {
                                                title: 'Door No.',
                                                key: 'door',
                                                align: 'center',
                                                width: 200
                                            }
                                        ]
                                    }
                                ]
                            }
                        ]
                    },
                    {
                        title: 'Company',
                        align: 'center',
                        children: [
                            {
                                title: 'Company Address',
                                key: 'caddress',
                                align: 'center',
                                width: 200
                            },
                            {
                                title: 'Company Name',
                                key: 'cname',
                                align: 'center',
                                width: 200
                            }
                        ]
                    },
                    {
                        title: 'Gender',
                        key: 'gender',
                        align: 'center',
                        width: 200,
                        fixed: 'right'
                    }
                ],
                data10: []
            }
        },
        mounted () {
            const data = [];
            for (let i = 0; i < 20; iPP) {
                data.push({
                    key: i,
                    name: 'John Brown',
                    age: i + 1,
                    street: 'Lake Park',
                    building: 'C',
                    door: 2035,
                    caddress: 'Lake Street 42',
                    cname: 'SoftLake Co',
                    gender: 'M',
                });
            }
            this.data10 = data;
        }
    }
</script>
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