vant-weapp/packages/index-bar/demo/index.ts

import { VantComponent } from '../../common/component';

const indexList: string[] = [];
const charCodeOfA = 'A'.charCodeAt(0);
for (let i = 0; i < 26; i++) {
  indexList.push(String.fromCharCode(charCodeOfA + i));
}

VantComponent({
  data: {
    activeTab: 0,
    indexList,
    customIndexList: [1, 2, 3, 4, 5, 6, 8, 9, 10],
    scrollTop: 0,
  },

  methods: {
    onChange(event) {
      this.setData({
        activeTab: event.detail.name,
      });
    },

    onPageScroll(event) {
      this.setData({
        scrollTop: event.scrollTop,
      });
    },
  },
});