The primary way of displaying the application’s content inside Mergado pages is through the use of IFRAME elements. Furthermore, these IFRAMEs are sandboxed to eliminate security risks that may arise from using potentially untrusted content inside IFRAMEs that are placed in the middle of Mergado’s own pages. Since sandboxed IFRAMEs cannot speak directly with the rest of the Mergado page and vice versa, some standard form of JavaScript communication between the app’s viewport and the page around it must be defined.

Such standard form of communication is represented by the Mergado App IFRAME API (MAIA) provided by Mergado platform. It is through this API that app’s viewport IFRAME and Mergado wrapper page can communicate with each other.

Important: Be advised that – since it provides some essential information about the contents of viewport, without which Mergado cannot display the IFRAME properly – the placement and usage of MAIA in all app’s pages and viewports is mandatory. Applications that don’t include MAIA (or any equivalent implementation) in their pages’ source code will be deemed unsatisfactory.


To use the MAIA in your app’s viewports simply include the appropriate script file provided by Mergado into your page’s HTML source. You can use either of these:


What it does by itself

  1. When the MessageAPI.js script is loaded: After the script is executed, a new global Mergado variable containing a singleton object representing MAIA is instantly available inside the app’s viewport.

  2. When the app’s IFRAME is loaded:

    • After its content is loaded (i.e. the IFRAME’s onload event is fired) Mergado wrapper page sends a “hello message” to the app’s IFRAME, which is instanteously intercepted by MAIA residing inside of it. MAIA then sends the height of viewport’s content back to Mergado wrapper page, which then can update IFRAME’s height appropriately and the whole content of app’s viewport will be visible.
    • All elements having a data-download="somefileurl" attribute will have a onclick event handler attached. When fired, a message will be sent to the wrapper page which will in turn display up a popup window with URL set to somefileurl. This is to overcome the limitations of Firefox browser, which is otherwise in most cases unwilling to start a file download from inside of an IFRAME.

What you can do with it

The Mergado object has a number of methods which can be used to better your application, improve its usability or overcome any limitations that are the result of strict handling of sandboxed IFRAMEs by web browsers.

Method Parameters Description
Mergado.startDownload(string url)
url: Target URL to start download from A new mini window will be popped up having target URL as its location. The window will be closed after 10 seconds; until then the target server has time to make a proper response. In this case most probably in a form of a file download.
Mergado.tellHeight([int heightInPixels])
Mergado.openWindow(string url)
url: Target page URL A new browser window will be opened having the target URL as its location. This window will NOT automatically close itself.
Mergado.scrollTo(int topInPixels)
topInPixels: Vertical scroll value, relative to app’s IFRAME viewport. Must be set in pixels. The browser’s absolute vertical scroll will be calculated automatically. Just set this Y value relative to your page.
Mergado.setAppRoute(string fullAppRoute)
fullAppRoute: Complete app route e.g. eshop/1/project/2/help/ The fullAppRoute parameter is than via JS method history.replaceState() apended into mergado URL as route query string. And if this URL is then invoked, this part is appended after app URL in IFRAME src attribute.
  1. App calls
  2. In Mergado URL is appended
  3. If this page is loaded then IFRAME src attribute is created from
    and query string route parameter
Mergado.tellHeight([int heightInPixels])
heightInPixels (optional): Can be set in pixels, 0 or undefined DEPRECATED

The wrapper page will set height of app’s viewport IFRAME to this number of pixels. If no height is passed, it will be determined automatically.

For newly created apps since Mergado redesign in Spring 2018 this is no longer necessary, as the app’s iframe spans almost entire browser viewport and uses its own scrolling.

Warning: Do not manually copy & paste contents of MessageAPI.js file into your page’s source code. Always include the remote MessageAPI.js script file provided by Mergado platform at or This way you can be sure you use the most up-to-date version of MAIA.