WebApps with LocalStorage and AppCache/Print

This learning resource focuses on print generated content in the WebApp. The content is considered as result of processing data totally with the browser without submission to a remote server (see design of an AppLSAC)

Demo Files for Printing in an AppLSAC

The repository Print4JS contains a list of examples that are generated for this repository as quickstart. The shell script scan_demos4readme.sh generated file ./src/readme/demos.md which are also included with PanDoc/Try. Check out the demos to explore the underlying principles of client-side printing with contacting a remote server.

pandoc 2.7.3

Print4JS - Print Page for JavaScript

The repository [1] is a fork of print.js and will be maintained as a learning resource for AppLSAC. Javascript code can be used to creates a print job from the browser. With the library print.js a WebApp is able to print specific browser content like

Form content,
Images in a canvas,
PDF files,
Content of a textarea,
... Javascript has as window.print() method of the window object of the browser, but this method allow the printing of content of the current browser window only. print.js allows printing of specific content elements by calling the window.print() function on new window, that contains the desired content only. This concept leads to the 4 main steps:
(Open Window) Open a new browser window,
(Create Content) write the content, that should be printed into the browser window with Javascript,
(Call Printer API) call the window.print() function for the generated browser window,
(Close Window) close the browser window

This repository was forked from print.js and inspired by developements of Rodrigo Vieira (Github User: crabbly). The repository is used learn about printing methods within a Javascript WebApps.

Print4JS Steps

The next steps describe the basic constituents of creating a print job within a WebApp. The following code shows the underlying software design.

<html>
<head></head>
<body>
    <input type="button" value="Open Print Window" onclick="openPrintWindow()" />
</body>
<script type="text/javascript">
    function openPrintWindow(pURL) {
        var print_win = window.open(pURL);
        print_win.focus();
        return print_win
    }

    function addPrintContent(pPrintWin,pContent) {
      // pContent = '<h1>Hello, World!</h1>';
      // append to document body
      pPrintWin.document.body.innerHTML += pContent;

    }
    // var vPrintWin = openPrintWindow('about:blank');
    var vPrintWin = openPrintWindow('printwindow.html');
    addPrintContent(vPrintWin,"<h1>Hello, World!</h1>");
    vPrintWin.print();

</script>
</html>

For application in a WebApp (e.g. AppLSAC use the library print.js.

Open Browser Window

the following HTML code shows a basic concept of opening a printer window.

// create a new printer window
var print_win = window.open('printwindow.html');
// set the focus to the browser window
print_win.focus();

Write Content to Browser Window

// create a new printer window
var print_win = window.open('printwindow.html');
// set the focus to the browser window
print_win.document.body.innerHTML += '<h1>Hello, World!</h1>';

Call Printer Dialog

Assume the window with the generated content in vPrintWin then the content can be submitted to the printer with the vPrintWin.print() command.

Close Printer Content Window

In general closing a window is called with window.close(). In this case we are closing the window with the Printer Content. The printer window can be closed with vPrintWin.close(), if the window was created/opened from the WebApp with Javascript (see also AppLSAC).

HTML Content of Printer Window

The following file shows the content of printwindow.html:

<html>
  <link href="css/print.css" rel="stylesheet">
  <head>
    <title>
      Printer Window
    </title>
  </head>
  <body>
  </body>
</html>

The style sheet css/print.css format the output to the desired layout (e.g. font size, fonts, ...)

Remark

The window of loaded HTML page itself cannot be closed with window.close(). This is not a bug. This a security feature, because web sites should not be able to close a browser window with all open tabs, because the user might loose the content of forms in that window.