Property 'removeDuplicates' does not exist on type

Question

ts代码提示错误

Error:(9, 32) TS2339: Property 'removeDuplicates' does not exist on type '{ created(): number; methods: { removeDuplicates(nums: []): 0; }; }'.
什么原因引起的，要怎么修改？

<script lang="ts">
  export default{
    created(): number {
      console.log('22222',this.removeDuplicates([1,4,7]))
    },
    methods:{
      removeDuplicates(nums:[]) {
        console.log('111111',nums);
        return nums.length
      },
    },
  }
</script>