ant-design/components/back-top/index.jsx

import React from 'react';
import Animate from 'rc-animate';
import Icon from '../icon';
import addEventListener from 'rc-util/lib/Dom/addEventListener';
import classNames from 'classnames';
import omit from 'object.omit';

function getScroll(target, top) {
  if (typeof window === 'undefined') {
    return 0;
  }

  const prop = top ? 'pageYOffset' : 'pageXOffset';
  const method = top ? 'scrollTop' : 'scrollLeft';
  const isWindow = target === window;

  let ret = isWindow ? target[prop] : target[method];
  // ie6,7,8 standard mode
  if (isWindow && typeof ret !== 'number') {
    ret = window.document.documentElement[method];
  }

  return ret;
}

export default class BackTop extends React.Component {

  static propTypes = {
    visibilityHeight: React.PropTypes.number,
    target: React.PropTypes.func,
  }

  static defaultProps = {
    onClick() {},
    visibilityHeight: 400,
    target() {
      return window;
    },
    prefixCls: 'ant-back-top',
  }

  constructor(props) {
    super(props);
    const scrollTop = getScroll(props.target(), true);
    this.state = {
      visible: scrollTop > props.visibilityHeight,
    };
  }

  scrollToTop = (e) => {
    if (e) e.preventDefault();
    this.setScrollTop(0);
    this.props.onClick(e);
  }

  setScrollTop(value) {
    const targetNode = this.props.target();
    if (targetNode === window) {
      document.body.scrollTop = value;
      document.documentElement.scrollTop = value;
    } else {
      targetNode.scrollTop = value;
    }
  }

  handleScroll = () => {
    const { visibilityHeight, target } = this.props;
    const scrollTop = getScroll(target(), true);
    this.setState({
      visible: scrollTop > visibilityHeight,
    });
  }

  componentDidMount() {
    this.scrollEvent = addEventListener(this.props.target(), 'scroll', this.handleScroll);
  }

  componentWillUnmount() {
    if (this.scrollEvent) {
      this.scrollEvent.remove();
    }
  }

  render() {
    const { prefixCls, className, children, ...otherProps } = this.props;
    const classString = classNames({
      [prefixCls]: true,
      [className]: !!className,
    });

    const defaultElement = (
      <div className={`${prefixCls}-content`}>
        <Icon className={`${prefixCls}-icon`} type="to-top" />
      </div>
    );

    // fix https://fb.me/react-unknown-prop
    const divProps = omit(otherProps, [
      'visibilityHeight',
    ]);

    return (
      <Animate component="" transitionName="fade">
        {
          this.state.visible ?
            <div {...divProps} className={classString} onClick={this.scrollToTop}>
              {children || defaultElement}
            </div>
          : null
        }
      </Animate>
    );
  }
}