ant-design-vue/components/vc-align/Align.jsx

import PropTypes from '../_util/vue-types';
import { alignElement, alignPoint } from 'dom-align';
import addEventListener from '../_util/Dom/addEventListener';
import { isWindow, buffer, isSamePoint, isSimilarValue, restoreFocus } from './util';
import { cloneElement } from '../_util/vnode.js';
import clonedeep from 'lodash/cloneDeep';
import { getSlot } from '../_util/props-util';

function getElement(func) {
  if (typeof func !== 'function' || !func) return null;
  return func();
}

function getPoint(point) {
  if (typeof point !== 'object' || !point) return null;
  return point;
}

export default {
  props: {
    childrenProps: PropTypes.object,
    align: PropTypes.object.isRequired,
    target: PropTypes.oneOfType([PropTypes.func, PropTypes.object]).def(() => window),
    monitorBufferTime: PropTypes.number.def(50),
    monitorWindowResize: PropTypes.bool.def(false),
    disabled: PropTypes.bool.def(false),
  },
  data() {
    this.aligned = false;
    return {};
  },
  mounted() {
    this.$nextTick(() => {
      this.prevProps = { ...this.$props };
      const props = this.$props;
      // if parent ref not attached .... use document.getElementById
      !this.aligned && this.forceAlign();
      if (!props.disabled && props.monitorWindowResize) {
        this.startMonitorWindowResize();
      }
    });
  },
  updated() {
    this.$nextTick(() => {
      const prevProps = this.prevProps;
      const props = this.$props;
      let reAlign = false;
      if (!props.disabled) {
        const source = this.$el;
        const sourceRect = source ? source.getBoundingClientRect() : null;

        if (prevProps.disabled) {
          reAlign = true;
        } else {
          const lastElement = getElement(prevProps.target);
          const currentElement = getElement(props.target);
          const lastPoint = getPoint(prevProps.target);
          const currentPoint = getPoint(props.target);
          if (isWindow(lastElement) && isWindow(currentElement)) {
            // Skip if is window
            reAlign = false;
          } else if (
            lastElement !== currentElement || // Element change
            (lastElement && !currentElement && currentPoint) || // Change from element to point
            (lastPoint && currentPoint && currentElement) || // Change from point to element
            (currentPoint && !isSamePoint(lastPoint, currentPoint))
          ) {
            reAlign = true;
          }

          // If source element size changed
          const preRect = this.sourceRect || {};
          if (
            !reAlign &&
            source &&
            (!isSimilarValue(preRect.width, sourceRect.width) || !isSimilarValue(preRect.height, sourceRect.height))
          ) {
            reAlign = true;
          }
        }
        this.sourceRect = sourceRect;
      }

      if (reAlign) {
        this.forceAlign();
      }

      if (props.monitorWindowResize && !props.disabled) {
        this.startMonitorWindowResize();
      } else {
        this.stopMonitorWindowResize();
      }
      this.prevProps = { ...this.$props, align: clonedeep(this.$props.align) };
    });
  },
  beforeDestroy() {
    this.stopMonitorWindowResize();
  },
  methods: {
    startMonitorWindowResize() {
      if (!this.resizeHandler) {
        this.bufferMonitor = buffer(this.forceAlign, this.$props.monitorBufferTime);
        this.resizeHandler = addEventListener(window, 'resize', this.bufferMonitor);
      }
    },

    stopMonitorWindowResize() {
      if (this.resizeHandler) {
        this.bufferMonitor.clear();
        this.resizeHandler.remove();
        this.resizeHandler = null;
      }
    },

    forceAlign() {
      const { disabled, target, align } = this.$props;
      if (!disabled && target) {
        const source = this.$el;

        let result;
        const element = getElement(target);
        const point = getPoint(target);

        // IE lose focus after element realign
        // We should record activeElement and restore later
        const activeElement = document.activeElement;

        if (element) {
          result = alignElement(source, element, align);
        } else if (point) {
          result = alignPoint(source, point, align);
        }
        restoreFocus(activeElement, source);
        this.aligned = true;
        this.$listeners.align && this.$listeners.align(source, result);
      }
    },
  },

  render() {
    const { childrenProps } = this.$props;
    const child = getSlot(this)[0];
    if (child && childrenProps) {
      return cloneElement(child, { props: childrenProps });
    }
    return child;
  },
};