print react element

To print react element, the “easier way” is using react-to-print, but if we want do it by ourself, how to? The basic idea is same as react-to-print, use a invisaible iframe, write the html to the iframe, then call the print of the iframe window.

Get the html of the element

Two options: 1: const html = ReactDOMServer.renderToStaticMarkup(element);, in most case, this should work and it is straightforward.

2: Sometimes ReactDOMServer have problem to render the element, we can use ReactDOM.render() to render the element into the iframe body. react-to-print did the same kind of trick. In this case, as the html is already rendered in the iframe.

Print

export const printHtml = html => {
  const oHideFrame = document.createElement("iframe");

  oHideFrame.style.position = "fixed";
  oHideFrame.style.right = "0";
  oHideFrame.style.bottom = "0";
  oHideFrame.style.width = "0";
  oHideFrame.style.height = "0";
  oHideFrame.style.border = "0";
  document.body.appendChild(oHideFrame);

  const pri = oHideFrame.contentWindow;
  pri.document.open();
  pri.document.write(`
  <html lang="en">
    <head>
      <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/semantic-ui/2.4.1/semantic.min.css" />
    </head>
    <body>${html}</body>
  </html>
`);
  pri.document.close();
  pri.focus();
  pri.print();
  document.body.removeChild(oHideFrame);
};

Above is the working code. Some thing I want to mention is that I see many other code using onLoad event of the iframe, but it is not reliable, especially when the iframe is invisible, that make the print content is blank ocasionally, so in my solution, it use synchronous method document.write and document.close, this will make sure the content have write to the iframe and safe to print.(But for images, it still a problem.)


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