效果

代码，存放位置 /utils/waterMark.js

//waterMark.js文件
 
let waterMark = {}
 
let setWaterMark = (str,str1) => {
  let id = '1.23452384164.123412416';
 
  if (document.getElementById(id) !== null) {
 
    //ui-table是table上的一个样式，一般水印显示在这个table上
    if(document.getElementsByClassName("ui-table")[0]){
    
      document.getElementsByClassName("ui-table")[0].removeChild(document.getElementById(id));
    }
  }
 
  //创建一个画布
  let can = document.createElement('canvas');
  //设置画布的长宽
  can.width = 400;
  can.height = 239;
 
  let cans = can.getContext('2d');
  //旋转角度
  cans.rotate(-55 * Math.PI / 550);
  //设置字体 和字体大小
  cans.font = '18px FZXiaoBiaoSong';
  //can.style.letterSpacing = '5px';
  //设置填充绘画的颜色、渐变或者模式
  cans.fillStyle = 'rgba(225, 221, 221, 0.35)';
  //设置文本内容的当前对齐方式
  cans.textAlign = 'left';
  //设置在绘制文本时使用的当前文本基线
  cans.textBaseline = 'Middle';
  //设置间距
  can.style.letterSpacing = '55px';
  cans.fillText(str1+"   "+str, can.width / 8, can.height / 2);
 
  let div = document.createElement('div');
  div.id = id;
  div.style.pointerEvents = 'none';
  div.style.top = '0';
  div.style.left = '0';
  div.style.position = 'absolute';
  div.style.zIndex = '100000';
  div.style.width = "100%";
  div.style.height = "100%";
  div.style.background = 'url(' + can.toDataURL('image/png') + ') left top repeat';
  if(document.getElementsByClassName("ui-table")[0]){
    document.getElementsByClassName("ui-table")[0].appendChild(div);
  }
  return id;
}
 
// 该方法只允许调用一次
waterMark.set = (str,str1) => {
  let id = setWaterMark(str,str1);
  setInterval(() => {
    if (document.getElementById(id) === null) {
      id = setWaterMark(str,str1);
    }
  }, 500);
  window.onresize = () => {
    setWaterMark(str,str1);
  };
}
 
export default waterMark;

main.js引用

import waterMark from '@/utils/waterMark.js';

Vue.prototype.$waterMark = waterMark

页面的生命周期调用

    mounted(){
        //添加水印
        this.$waterMark.set(moment(new Date()).format('yyyy-MM-DD HH:mm:ss'),sessionStorage.getItem('realname'))
        
    },