React 照片预览，可放大缩小拖动

import React, { PureComponent } from "react";

let params = {
  zoomVal: 1,
  left: 0,
  top: 0,
  currentX: 0,
  currentY: 0,
  flag: false
};

export default class PhotoPreview extends PureComponent {
  componentDidMount() {
    this.startDrag(
      document.getElementById("img"),
      document.getElementById("img")
    );
  }

  //图片缩放
  onWheel = () => {
    // eslint-disable-next-line no-restricted-globals
    params.zoomVal += event.wheelDelta / 1200;
    if (params.zoomVal >= 0.2) {
      this.imgDom.style.transform = "scale(" + params.zoomVal + ")";
    } else {
      params.zoomVal = 0.2;
      this.imgDom.style.transform = "scale(" + params.zoomVal + ")";
      return false;
    }
  };

  //获取相关CSS属性
  getCss = (o, key) => {
    return o.currentStyle
      ? o.currentStyle[key]
      : document.defaultView.getComputedStyle(o, false)[key];
  };

  //拖拽的实现
  startDrag = (bar, target, callback) => {
    if (this.getCss(target, "left") !== "auto") {
      params.left = this.getCss(target, "left");
    }
    if (this.getCss(target, "top") !== "auto") {
      params.top = this.getCss(target, "top");
    }
    //o是移动对象
    bar.onmousedown = event => {
      params.flag = true;
      if (!event) {
        event = window.event;
        //防止IE文字选中
        bar.onselectstart = () => {
          return false;
        };
      }
      var e = event;
      params.currentX = e.clientX;
      params.currentY = e.clientY;
    };

    document.onmouseup = () => {
      params.flag = false;
      if (this.getCss(target, "left") !== "auto") {
        params.left = this.getCss(target, "left");
      }
      if (this.getCss(target, "top") !== "auto") {
        params.top = this.getCss(target, "top");
      }
    };

    document.onmousemove = event => {
      var e = event ? event : window.event;

      if (params.flag) {
        var nowX = e.clientX,
          nowY = e.clientY;
        var disX = nowX - params.currentX,
          disY = nowY - params.currentY;
        target.style.left = parseInt(params.left, 10) + disX + "px";
        target.style.top = parseInt(params.top, 10) + disY + "px";

        if (typeof callback === "function") {
          callback(
            (parseInt(params.left, 10) || 0) + disX,
            (parseInt(params.top, 10) || 0) + disY
          );
        }

        if (event.preventDefault) {
          event.preventDefault();
        }
        return false;
      }
    };
  };

  render() {
    const { src } = this.props;
    return (
      

         {
            this.imgDom = dom;
          }}
          style={{
            position: "absolute",
            width: "100%",
            height: "auto",
            cursor: "move"
          }}
        />
      
    );
  }
}