yiyunjianzhuBeta/node_modules/vuetify/lib/mixins/scrollable/index.js

// Directives
import { Scroll } from '../../directives'; // Utilities

import { consoleWarn } from '../../util/console'; // Types

import Vue from 'vue';
/**
 * Scrollable
 *
 * Used for monitoring scrolling and
 * invoking functions based upon
 * scrolling thresholds being
 * met.
 */

/* @vue/component */

export default Vue.extend({
  name: 'scrollable',
  directives: {
    Scroll
  },
  props: {
    scrollTarget: String,
    scrollThreshold: [String, Number]
  },
  data: () => ({
    currentScroll: 0,
    currentThreshold: 0,
    isActive: false,
    isScrollingUp: false,
    previousScroll: 0,
    savedScroll: 0,
    target: null
  }),
  computed: {
    /**
     * A computed property that returns
     * whether scrolling features are
     * enabled or disabled
     */
    canScroll() {
      return typeof window !== 'undefined';
    },

    /**
     * The threshold that must be met before
     * thresholdMet function is invoked
     */
    computedScrollThreshold() {
      return this.scrollThreshold ? Number(this.scrollThreshold) : 300;
    }

  },
  watch: {
    isScrollingUp() {
      this.savedScroll = this.savedScroll || this.currentScroll;
    },

    isActive() {
      this.savedScroll = 0;
    }

  },

  mounted() {
    if (this.scrollTarget) {
      this.target = document.querySelector(this.scrollTarget);

      if (!this.target) {
        consoleWarn(`Unable to locate element with identifier ${this.scrollTarget}`, this);
      }
    }
  },

  methods: {
    onScroll() {
      if (!this.canScroll) return;
      this.previousScroll = this.currentScroll;
      this.currentScroll = this.target ? this.target.scrollTop : window.pageYOffset;
      this.isScrollingUp = this.currentScroll < this.previousScroll;
      this.currentThreshold = Math.abs(this.currentScroll - this.computedScrollThreshold);
      this.$nextTick(() => {
        if (Math.abs(this.currentScroll - this.savedScroll) > this.computedScrollThreshold) this.thresholdMet();
      });
    },

    /**
     * The method invoked when
     * scrolling in any direction
     * has exceeded the threshold
     */
    thresholdMet() {}

  }
});
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