elementUI ＜el-input＞输入框只能输入正整数

<template>
  <div class="app">
    <el-form ref="form" :model="form" label-width="80px">
      <el-input v-model="form.num" type="text" @input="changeInput" />
    </el-form>
  </div>
</template>
<script>
export default {
  data() {
    return {
      form: {
        num: ''
      }
    }
  },
  methods: {
    changeInput() {
      var pattern = /^[1-9][0-9]*$/
      if (!pattern.test(this.form.num)) {
        this.form.num = ''
      }
    }
  }
}
</script>