如何使用makepdf将Web worker应用于渲染PDF

Question

我使用JavaScript插件(pdfmake)成功创建了一个PDF ,非常棒.但是当我尝试渲染~8,000行的库存/分类帐打印输出时,它会冻结超过一分钟.

这就是我通常声明我的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' }] }

哪里

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}]

产生 .

我搜索了网络工作者,看到它可以解决这个UI冻结问题.所以我尝试为它创建一个Web worker:

$('#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);

输出来自console.log():

工作者说:对象{pageOrientation:"portrait",content:Array [7]}它正确记录了json结构.

到现在为止还挺好.但之后,我加入pdfmake.min.js并vfs_font.js给工人,我得到的错误Uncaught TypeError: Cannot read property 'createElementNS' of undefined.

在我开始使用worker之前我得到了错误.

是否可以使用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,如果您认为它太脏了,请导入XML-JS(仅60k)并为pdfmake创建虚拟文档.

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

说明

众所周知,pdfmake 与工人不相容.

pdfmake 本身不使用 createElementNS.然而,它的缩小脚本pdfmake.min.js确实可以创建一个下载链接.

我们无论如何都不需要下载链接,所以只需给它一个假人来保持它的快乐(现在).

如果将来它需要一个真正的DOM,坏消息就是web worker中没有文档.好消息是我们有一个纯粹的JavaScript实现. 下载 XML-JS,提取并查找tinyxmlw3cdom.js,导入它,您可以创建一个功能文档.

除了文档之外,由于vfs_fonts.js通过window变量获取pdfmake ,我们需要引入window作为global的别名.

对我来说,这些步骤使pdfmake在web worker中起作用.

要保存文件,您需要将pdfmake提供的base64数据转换为二进制下载.有许多脚本可供使用,例如download.js.在下面的代码中我使用的是FileSaver.

码

我的worker是一个可以缓存的Builder.如果你在服务器端组合工作者,你可以摆脱堆栈并构建函数并直接调用pdfmake,使得两个js代码更加简单.

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;
   }
};

})();