vant-weapp/packages/mixins/touch.ts

import { Weapp } from "definitions/weapp";

export const touch = Behavior({
  methods: {
    touchStart(event: Weapp.TouchEvent) {
      const touch = event.touches[0];
      this.direction = '';
      this.deltaX = 0;
      this.deltaY = 0;
      this.offsetX = 0;
      this.offsetY = 0;
      this.startX = touch.clientX;
      this.startY = touch.clientY;
    },

    touchMove(event: Weapp.TouchEvent) {
      const touch = event.touches[0];
      this.deltaX = touch.clientX - this.startX;
      this.deltaY = touch.clientY - this.startY;
      this.offsetX = Math.abs(this.deltaX);
      this.offsetY = Math.abs(this.deltaY);
      this.direction =
        this.offsetX > this.offsetY
          ? 'horizontal'
          : this.offsetX < this.offsetY
            ? 'vertical'
            : '';
    }
  }
});