vant-weapp/packages/mixins/transition.ts

import { isObj } from '../common/utils';

const getClassNames = (name: string) => ({
  enter: `van-${name}-enter van-${name}-enter-active enter-class enter-active-class`,
  'enter-to': `van-${name}-enter-to van-${name}-enter-active enter-to-class enter-active-class`,
  leave: `van-${name}-leave van-${name}-leave-active leave-class leave-active-class`,
  'leave-to': `van-${name}-leave-to van-${name}-leave-active leave-to-class leave-active-class`
});

const nextTick = () => new Promise(resolve => setTimeout(resolve, 1000 / 30));

export const transition = function(showDefaultValue: boolean) {
  return Behavior({
    properties: {
      customStyle: String,
      show: {
        type: Boolean,
        value: showDefaultValue,
        // @ts-ignore
        observer: 'observeShow'
      },
      duration: {
        type: null,
        value: 300,
        // @ts-ignore
        observer: 'observeDuration'
      },
      name: {
        type: String,
        value: 'fade'
      }
    },

    data: {
      type: '',
      inited: false,
      display: false
    },

    methods: {
      observeShow(value: boolean, old: boolean) {
        if (value === old) {
          return;
        }
        value ? this.enter() : this.leave();
      },

      enter() {
        const { duration, name } = this.data;
        const classNames = getClassNames(name);
        const currentDuration = isObj(duration) ? duration.enter : duration;

        this.status = 'enter';
        this.$emit('before-enter');

        Promise.resolve()
          .then(nextTick)
          .then(() => {
            this.checkStatus('enter');
            this.$emit('enter');

            this.setData({
              inited: true,
              display: true,
              classes: classNames.enter,
              currentDuration
            });
          })
          .then(nextTick)
          .then(() => {
            this.checkStatus('enter');
            this.transitionEnded = false;

            this.setData({
              classes: classNames['enter-to']
            });
          })
          .catch(() => {});
      },

      leave() {
        if (!this.data.display) {
          return;
        }

        const { duration, name } = this.data;
        const classNames = getClassNames(name);
        const currentDuration = isObj(duration) ? duration.leave : duration;

        this.status = 'leave';
        this.$emit('before-leave');

        Promise.resolve()
          .then(nextTick)
          .then(() => {
            this.checkStatus('leave');
            this.$emit('leave');

            this.setData({
              classes: classNames.leave,
              currentDuration
            });
          })
          .then(nextTick)
          .then(() => {
            this.checkStatus('leave');
            this.transitionEnded = false;
            setTimeout(() => this.onTransitionEnd(), currentDuration);

            this.setData({
              classes: classNames['leave-to']
            });
          })
          .catch(() => {});
      },

      checkStatus(status: 'enter' | 'leave') {
        if (status !== this.status) {
          throw new Error(`incongruent status: ${status}`);
        }
      },

      onTransitionEnd() {
        if (this.transitionEnded) {
          return;
        }

        this.transitionEnded = true;
        this.$emit(`after-${this.status}`);

        const { show, display } = this.data;
        if (!show && display) {
          this.setData({ display: false });
        }
      }
    }
  });
};