react实现拖拽

import React from 'react'

export default class extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      translateX: 0,
      translateY: 0,
    };
  }
  small_down=(e)=> {
    var obig = this.refs.move.parentNode;
    var osmall = this.refs.move;
    var e = e || window.event;
    /*用于保存小的div拖拽前的坐标*/
    osmall.startX = e.clientX - osmall.offsetLeft;
    osmall.startY = e.clientY - osmall.offsetTop;
    /*鼠标的移动事件*/
    document.onmousemove = function(e) {
      var e = e || window.event;
      osmall.style.left = e.clientX - osmall.startX + "px";
      osmall.style.top = e.clientY - osmall.startY + "px";
      /*对于大的DIV四个边界的判断*/
      let x=obig.offsetWidth-osmall.offsetWidth
      let y=obig.offsetHeight-osmall.offsetHeight
      if (e.clientX - osmall.startX <= 0) {
        osmall.style.left = 0 + "px";
      }
      if (e.clientY - osmall.startY <= 0) {
        osmall.style.top = 0 + "px";
      }
      if (e.clientX - osmall.startX >= x) {
        osmall.style.left = x + "px";
      }
      if (e.clientY - osmall.startY >= y) {
        osmall.style.top = y + "px";
      }
    };
    /*鼠标的抬起事件,终止拖动*/
    document.onmouseup = function() {
      document.onmousemove = null;
      document.onmouseup = null;
    };
  }
  componentDidMount(){

  }
  render() {
    return (
      <div
        style={{ "500px" ,height:"500px" ,background:"red" ,margin:"0 auto" ,position:"relative"}}
      >
        <div ref="move" onMouseDown={e => this.small_down(e)} style={{position:"absolute", left: `${this.state.translateX}px`,top:`${this.state.translateY}px`,  100, height: 100, backgroundColor: 'blue', }} />
      </div>
    )
  }
};