vant/src/mixins/touch.ts

import Vue from 'vue';
import { on } from '../utils/dom/event';

const MIN_DISTANCE = 10;

function getDirection(x: number, y: number) {
  if (x > y && x > MIN_DISTANCE) {
    return 'horizontal';
  }

  if (y > x && y > MIN_DISTANCE) {
    return 'vertical';
  }

  return '';
}

type TouchMixinData = {
  startX: number;
  startY: number;
  deltaX: number;
  deltaY: number;
  offsetX: number;
  offsetY: number;
  direction: string;
};

export const TouchMixin = Vue.extend({
  data() {
    return { direction: '' } as TouchMixinData;
  },

  methods: {
    touchStart(event: TouchEvent) {
      this.resetTouchStatus();
      this.startX = event.touches[0].clientX;
      this.startY = event.touches[0].clientY;
    },

    touchMove(event: 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.direction || getDirection(this.offsetX, this.offsetY);
    },

    resetTouchStatus() {
      this.direction = '';
      this.deltaX = 0;
      this.deltaY = 0;
      this.offsetX = 0;
      this.offsetY = 0;
    },

    // avoid Vue 2.6 event bubble issues by manually binding events
    // https://github.com/youzan/vant/issues/3015
    bindTouchEvent(el: HTMLElement) {
      const { onTouchStart, onTouchMove, onTouchEnd } = this as any;

      on(el, 'touchstart', onTouchStart);
      on(el, 'touchmove', onTouchMove);

      if (onTouchEnd) {
        on(el, 'touchend', onTouchEnd);
        on(el, 'touchcancel', onTouchEnd);
      }
    },
  },
});