Javascript: parent.framename.document.forms[i].elements.length

I have a PHP-Script 1 with an iframe. In this iframe an other PHP-Script 2 is loaded, which contains several forms. In one of this forms I make a call by button with onclick="..." to a javascript-function. The javascript-function is contained in an external file *.js. Declaration in PHP-Script 2: <Script type="text/javascript" src="WartArtikel-Probe.js"></Script>. Inside the javascript-function I use: Scenario 1: var i = 0; var anzelem = parent.framename.document.forms[i].elements.length; or: var anzelem = parent.frames[0].document.forms[i].elements.length; or: var anzelem = window.document.forms[i].elements.length; When I press the button, the javascript-function gives no answer. But when I start PHP-Script 2 directly (not inside an iframe) and the javascript-function is written as: Scenario 2: var i = 0; var anzelem = document.forms[i].elements.length; this example works! How can I get an answer in scenario 1? Additional suggestion: Is it possible to switch the browser into a development-modus, where javascript-syntax-errors are displayed? This could be very helpful!