Recently, I have been printing reports in vue + elemnet, and then there is a demand to print the charts directly. After downloading the printing plug-in, I found that the chart part of the charts on the printing page is blank. After careful inspection, I found that the plug-in does not support printing canvas. Later, I found the following js on the Internet, but added canvas to the original js code. Properties, see below for details

// Print class property and method definition
/* 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')
            }
          }
        }
      }
    }
    //Canvas echars chart to picture
    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);
    }
    //Paging
    //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. Add instance method
  Vue.prototype.$print = Print
}
export default MyPlugin

If the plug-in is imported directly, it will directly report that the clientWidth is not defined, so we need to proceed to the next step:

<el-button type="primary" class="results" @click="generateReport">Printing</el-button>

The class name here should be consistent with that in the plug-in. OK, let's see the effect.

Well, that's what I want~~

Original link: https://blog.csdn.net/shishuwei111/article/details/94167974