Access a variable of iframe from parent

Question

script of iframe

<script type="text/javascript" > var a=5; </script> 

script of parent window

<script type="text/javascript" > function close() { var check=document.getElementById("iframeid").contentDocument.a; alert(check) } </script> 

I want to access the variable which is defined inside the iframe from parent. But the above code doesn't work properly can anyone give an idea to implement this.

Answer 1

Using contentWindow instead of contentDocument works for me:

var check = document.getElementById("iframeid").contentWindow.a; 

Also, ensure that the domains match and that you are using a webserver to test (I got a protocol warning when testing from the file system).

UPDATE: You're almost definitely better to use the postMessage API.

Answer 2

One method that has always worked reliably for me is for the iFrame to give its parent a reference to its own window when it first loads. The parent can then access all the variables through that reference. This does require that the parent is loaded before the iFrame, but for me that is usually the case.

So in the parent

var iFrameWin; 

Then in the iFrame at some point after it has loaded and settled down

parent.iFrameWin = window;  //parent now has a ref to the iframe's window 

Then, in the parent when it wants a global var contents from the iFrame

alert(iFrameWin.ivar);  // shows value if the global 'ivar' in the iFrame