The issue you're encountering with the print preview coming up empty might be due to the timing of the window.print() function. The DOM might not be fully rendered or updated when the print command is triggered. Here are a few steps you can take to ensure the HTML content is properly rendered before the print preview is triggered:

Possible Solutions

1. Ensure the DOM is Fully Updated:
   • Instead of using a simple setTimeout, you can use requestAnimationFrame to ensure that the DOM update has been fully rendered before triggering the print.

   javascriptCopy codeasync _printWeb(receipt) {
       try {
           const receiptContainer = $(this.el).find('.pos-cash-rpt-container');
   
           receiptContainer.empty();
           receiptContainer.html(receipt);
   
           // Wait for the next frame to ensure the DOM is updated
           await new Promise(resolve => requestAnimationFrame(resolve));
   
           window.print();
       } catch (_err) {
           await this.showPopup('ErrorPopup', {
               title: this.env._t('Printing is not supported on some browsers'),
               body: this.env._t(
                   'Printing is not supported on some browsers due to no default printing protocol ' +
                   'is available. It is possible to print your tickets by making use of an IoT Box.'
               ),
           });
       }
   }
   

2. Force a Reflow Before Printing:
   • Sometimes, forcing a reflow of the document can help ensure that all changes are rendered before printing. You can do this by accessing certain properties (like offsetHeight) that trigger a reflow.

   javascriptCopy codeasync _printWeb(receipt) {
       try {
           const receiptContainer = $(this.el).find('.pos-cash-rpt-container');
   
           receiptContainer.empty();
           receiptContainer.html(receipt);
   
           // Force reflow
           receiptContainer[0].offsetHeight;
   
           await new Promise((resolve) => setTimeout(resolve, 100));
   
           window.print();
       } catch (_err) {
           await this.showPopup('ErrorPopup', {
               title: this.env._t('Printing is not supported on some browsers'),
               body: this.env._t(
                   'Printing is not supported on some browsers due to no default printing protocol ' +
                   'is available. It is possible to print your tickets by making use of an IoT Box.'
               ),
           });
       }
   }
   

3. Check for Browser Compatibility:
   • Make sure that the browser you're using supports the window.print() function as expected. Sometimes, certain browsers might have issues with printing, especially in a POS environment. Testing on different browsers can help identify if the problem is browser-specific.
4. Debugging the Receipt Container:
   • Add some logging or debugging to ensure that the receiptContainer.html(receipt) is indeed populating the container with the correct content before printing.

   javascriptCopy codeconsole.log(receipt); // Check if the receipt content is correct
   console.log(receiptContainer.html()); // Check if the container is populated with the content
   

If the print preview continues to show up empty after trying these solutions, you may need to explore alternative approaches to printing, such as using the Odoo IoT Box for more reliable printing in POS environments.