如何使用 web worker 使用 makepdf 渲染 PDF

Question

我使用 JavaScript 插件 (pdfmake) 成功创建了一个 PDF，它很棒。但是当我尝试渲染 ~8,000 行 inventory/ledger 打印输出时，它冻结了一分钟多。

这就是我通常声明 docDefinition 的方式

var docDefinition = { 
pageOrientation: orientation, 
footer: function(currentPage, pageCount) { return {text: currentPage.toString() + ' / ' + pageCount, fontSize:8, alignment:'center'}; }, 
content:[ 
   printHeader, 
  { fontSize: 8, alignment: 'right', style: 'tableExample', 
   table: { 
       widths: width, 
       headerRows: 1, body: arr }, 
   layout: 'lightHorizontalLines' }] }

其中

var printHeader =   [ { text: 'COMPANY NAME',alignment:'center' },
{ text: 'Address 1',alignment:'center' },
{ text: 'Address 2',alignment:'center' },
{ text: 'Additional Details,alignment:'center' },
{ text: 'document title',alignment:'center' }];

和

 var arr = [[{"text":"","alignment":"left"},"text":"Date","alignment":"left"},
{"text":"Trans #","alignment":"left"},{"text":"Description","alignment":"left"},
{"text":"Ref #","alignment":"left"},{"text":"Debit","alignment":"left"},
{"text":"Credit","alignment":"left"},{"text":"Amount","alignment":"left"},
{"text":"Balance","alignment":"left"}],[{"text":"ACCOUNT : Merchandise Inventory","alignment":"left","colSpan":8},"","","","","","","",
{"text":"1,646,101.06"}],["","10/13/2015","ST#0094",{"text":"","alignment":"left"},{"text":"","alignment":"left"},"546.94","0.00","546.94","1,646,648.00"],[{"text":"Total","alignment":"left","bold":true},"","","","",
{"text":"546.94","alignment":"right","bold":true},
{"text":"0.00","alignment":"right","bold":true},
{"text":"","alignment":"right","bold":true},
{"text":"546.94","alignment":"right","bold":true}],[{"text":"ACCOUNT : Accounts Payable-Main","alignment":"left","colSpan":8},"","","","","","","",
{"text":"-1,741,953.62"}],["","10/13/2015","ST#0094",
{"text":"","alignment":"left"},
{"text":"","alignment":"left"},"0.00","546.94","-546.94","-1,742,500.56"],
[{"text":"Total","alignment":"left","bold":true},"","","","",
{"text":"0.00","alignment":"right","bold":true},
{"text":"546.94","alignment":"right","bold":true},
{"text":"","alignment":"right","bold":true},
{"text":"-546.94","alignment":"right","bold":true}]

生成了.

我搜索了 web workers，发现它可以解决这个 UI 冻结问题。所以我尝试为它创建一个网络工作者：

$('#makepdf').click(function(){
    var worker = new Worker("<?php echo URL::to('/'); ?>/js/worker.js");
  worker.addEventListener('message',function(e){
  console.log('Worker said: ',e.data);
},false);

worker.postMessage(docDefinition);

//worker.js

self.addEventListener('message', function(e) {
  self.postMessage(e.data);
}, false);

来自console.log()的输出：

Worker said: Object {pageOrientation: "portrait", content: Array[7]} its logging correctly the json structure.

到目前为止一切顺利。但是在我将 pdfmake.min.js 和 vfs_font.js 添加到 worker 之后，我得到了错误 Uncaught TypeError: Cannot read property 'createElementNS' of undefined.

我什至在开始使用 worker 之前就收到错误消息。

能否用pdfmake插件实现web worker？

Answer 1

简单回答

只需提供一个虚拟构造函数：

var document = { 'createElementNS': function(){ return {} } };
var window = this;
importScripts( 'pdfmake.min.js', 'vfs_fonts.js' );

或者，如果您认为它太脏，请导入 XML-JS (only 60k) and create a virtual document for pdfmake。

importScripts( 'tinyxmlw3cdom.js' );
var window = this;
var document = new DOMDocument( new DOMImplementation() );
importScripts( 'pdfmake.min.js', 'vfs_fonts.js' );

说明

已知 pdfmake 与工人 incompatible。

pdfmake does not use createElementNS 本身。然而它的缩小脚本 pdfmake.min.js 确实如此，显然是为了创建一个下载 link.

无论如何我们都不需要下载 link，所以只是给它一个假人让它开心（暂时）。

如果将来需要一个真正的 DOM, 坏消息是 web worker 中的文档是 unavailable。好消息是我们有一个纯粹的 javascript 实现。 Download XML-JS, 提取并找到 tinyxmlw3cdom.js, 导入它，你可以创建一个功能文档。

除了文档，由于vfs_fonts.js通过window变量获取pdfmake，所以需要引入window作为global的别名

对我来说，这些步骤使 pdfmake 在 web worker 中工作。

保存文件需要将pdfmake提供的base64数据转换成二进制下载。有许多脚本可用，例如 download.js。在下面的代码中，我使用 FileSaver.

代码

我的worker是一个可以缓存的Builder。如果您在服务器端组成工作人员，你可以摆脱堆栈和构建函数并直接调用pdfmake，使两个 js 代码更简单。

主要HTML:

<script src='FileSaver.min.js'></script>
<script>
function base64ToBlob( base64, type ) {
    var bytes = atob( base64 ), len = bytes.length;
    var buffer = new ArrayBuffer( len ), view = new Uint8Array( buffer );
    for ( var i=0 ; i < len ; i++ )
      view[i] = bytes.charCodeAt(i) & 0xff;
    return new Blob( [ buffer ], { type: type } );
}
//////////////////////////////////////////////////////////

var pdfworker = new Worker( 'worker.js' );

pdfworker.onmessage = function( evt ) {
   // open( 'data:application/pdf;base64,' + evt.data.base64 ); // Popup PDF
   saveAs( base64ToBlob( evt.data.base64, 'application/pdf' ), 'General Ledger.pdf' );
};

function pdf( action, data ) {
   pdfworker.postMessage( { action: action, data: data } );
}

pdf( 'add', 'Hello WebWorker' );
pdf( 'add_table', { headerRows: 1 } );
pdf( 'add', [ 'First', 'Second', 'Third', 'The last one' ] );
pdf( 'add', [ { text: 'Bold value', bold: true }, 'Val 2', 'Val 3', 'Val 4' ] );
pdf( 'close_table' );
pdf( 'add', { text: 'This paragraph will have a bigger font', fontSize: 15 } );
pdf( 'gen_pdf' ); // Triggers onmessage when it is done

// Alternative, one-size-fit-all usage
pdf( 'set', { pageOrientation: 'landscape', footer: { text: 'copyright 2015', fontSize: 8, alignment:'center'}, content:[ "header", { fontSize: 8, alignment: 'right', table: { headerRows: 1, body: [[1,2,3],[4,5,6]] } }] } );
pdf( 'gen_pdf' );

</script>

工人：

//importScripts( 'tinyxmlw3cdom.js' );
//var document = new DOMDocument( new DOMImplementation() );
var document = { 'createElementNS': function(){ return {} } };
var window = this;
importScripts( 'pdfmake.min.js', 'vfs_fonts.js' );

(function() { 'use strict';

var doc, current, context_stack;

function set ( data ) {
   doc = data;
   if ( ! doc.content ) doc.content = [];
   current = doc.content;
   context_stack = [ current ];
}
set( {} );

function add ( data ) {
   current.push( data );
}

function add_table ( template ) {
   if ( ! template ) template = {};
   if ( ! template.table ) template = { table: template };
   if ( ! template.table.body ) template.table.body = [];
   current.push( template ); // Append table
   push( template.table.body ); // Switch context to table body
}

function push ( data ) {
   context_stack.push( current );
   return current = data;
}

function pop () {
   if ( context_stack.length <= 1 ) return console.warn( "Cannot close pdf root" );
   context_stack.length -= 1;
   return current = context_stack[ context_stack.length-1 ];
}

function gen_pdf() {
   pdfMake.createPdf( doc ).getBase64( function( base64 ) {
      postMessage( { action: 'gen_pdf', base64: base64 } );
   } );
}

onmessage = function( evt ) {
   var action = evt.data.action, data = evt.data.data;
   switch ( action ) {
      case 'set': set( data ); break;
      case 'add': add( data ); break;
      case 'add_table'  : add_table( data ); break;
      case 'close_table': pop(); break;
      case 'gen_pdf': gen_pdf(); break;
   }
};

})();

如何使用 web worker 使用 makepdf 渲染 PDF

How to apply web worker to rendering of a PDF using makepdf

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pdfmake