vue 打印 canvas 显示空白

最近在弄 vue + elemnet 打印报表，然后有个需求就是直接打印将 echarts 表也打印出来，我下载上打印插件后，在打印页面发现 echarts 图表部分为空白，再仔细检查发现这个插件不支持打印canvas，后来我又在网上找到下面这个js，只是在原先的 js 代码上又增加了 canvas 属性，详情请看下方

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

// 打印类属性、方法定义
/* eslint-disable */
const Print = function (dom, options) {
  if (!(this instanceof Print)) return new Print(dom, options);
  
  this.options = this.extend({
    'noPrint': '.no-print'
  }, options);
  
  if ((typeof dom) === "string") {
    this.dom = document.querySelector(dom);
  } else {
    this.isDOM(dom)
    this.dom = this.isDOM(dom) ? dom : dom.$el;
  }
  
  this.init();
};
Print.prototype = {
  init: function () {
    var content = this.getStyle() + this.getHtml();
    this.writeIframe(content);
  },
  extend: function (obj, obj2) {
    for (var k in obj2) {
      obj[k] = obj2[k];
    }
    return obj;
  },
  
  getStyle: function () {
    var str = "",
      styles = document.querySelectorAll('style,link');
    for (var i = 0; i < styles.length; i++) {
      str += styles[i].outerHTML;
    }
    str += "<style>" + (this.options.notPrint ? this.options.notPrint : '.no-print') + "{display:none;}</style>";
    str += "<style>.results{width:100%!important;} .result .title{width:100%;}</style>";
  
    return str;
  },
  
  getHtml: function () {
    var inputs = document.querySelectorAll('input');
    var textareas = document.querySelectorAll('textarea');
    var selects = document.querySelectorAll('select');
    var canvass = document.querySelectorAll('canvas');
    for (var k = 0; k < inputs.length; k++) {
      if (inputs[k].type == "checkbox" || inputs[k].type == "radio") {
        if (inputs[k].checked == true) {
          inputs[k].setAttribute('checked', "checked")
        } else {
          inputs[k].removeAttribute('checked')
        }
      } else if (inputs[k].type == "text") {
        inputs[k].setAttribute('value', inputs[k].value)
      } else {
        inputs[k].setAttribute('value', inputs[k].value)
      }
    }
  
    for (var k2 = 0; k2 < textareas.length; k2++) {
      if (textareas[k2].type == 'textarea') {
        textareas[k2].innerHTML = textareas[k2].value
      }
    }
  
    for (var k3 = 0; k3 < selects.length; k3++) {
      if (selects[k3].type == 'select-one') {
        var child = selects[k3].children;
        for (var i in child) {
          if (child[i].tagName == 'OPTION') {
            if (child[i].selected == true) {
              child[i].setAttribute('selected', "selected")
            } else {
              child[i].removeAttribute('selected')
            }
          }
        }
      }
    }
    //canvass echars图表转为图片
    for (var k4 = 0; k4 < canvass.length; k4++) {
      var imageURL = canvass[k4].toDataURL("image/png");
      var img = document.createElement("img");
      img.src = imageURL;
      img.setAttribute('style', 'max-width: 100%;');
      img.className = 'isNeedRemove'
      // canvass[k4].style.display = 'none'
      // canvass[k4].parentNode.style.width = '100%'
      // canvass[k4].parentNode.style.textAlign = 'center'
      canvass[k4].parentNode.insertBefore(img,canvass[k4].nextElementSibling);
    }
    //做分页
    //style="page-break-after: always"
    var pages = document.querySelectorAll('.result');
    for (var k5 = 0; k5 < pages.length; k5++) {
      pages[k5].setAttribute('style', 'page-break-after: always');
    }
    return this.dom.outerHTML;
  },
  
  writeIframe: function (content) {
    var w, doc, iframe = document.createElement('iframe'),
      f = document.body.appendChild(iframe);
    iframe.id = "myIframe";
    //iframe.style = "position:absolute;width:0;height:0;top:-10px;left:-10px;";
    iframe.setAttribute('style', 'position:absolute;width:' + document.querySelector('.results').clientWidth + 'px;height:0;top:-10px;left:-10px;');
    w = f.contentWindow || f.contentDocument;
    doc = f.contentDocument || f.contentWindow.document;
    doc.open();
    doc.write(content);
    doc.close();
  
    var removes = document.querySelectorAll('.isNeedRemove');
    for (var k = 0; k < removes.length; k++) {
      removes[k].parentNode.removeChild(removes[k]);
    }
  
    var _this = this
    iframe.onload = function(){
      _this.toPrint(w);
      setTimeout(function () {
        document.body.removeChild(iframe)
      }, 100)
    }
  },
  
  toPrint: function (frameWindow) {
    try {
      setTimeout(function () {
        frameWindow.focus();
        try {
          if (!frameWindow.document.execCommand('print', false, null)) {
            frameWindow.print();
          }
        } catch (e) {
          frameWindow.print();
        }
        frameWindow.close();
      }, 10);
    } catch (err) {
      console.log('err', err);
    }
  },
  isDOM: (typeof HTMLElement === 'object') ?
    function (obj) {
      return obj instanceof HTMLElement;
    } :
    function (obj) {
      return obj && typeof obj === 'object' && obj.nodeType === 1 && typeof obj.nodeName === 'string';
    }
};
const MyPlugin = {}
MyPlugin.install = function (Vue, options) {
  // 4. 添加实例方法
  Vue.prototype.$print = Print
}
export default MyPlugin