why am I so bad at JS? (nonfunctional chat macro)

as a chat marco:
/goto inventory.php?ftext=___'; top.mainpane.location.onunload = function(){ top.mainpane.frameElement.contentDocument.forms[2].children[0].value += 'boop' } ; z='

as an equivalent(?) javascript...script?

top.mainpane.location = 'inventory.php?ftext=___';
top.mainpane.location.onunload = function(){
top.mainpane.frameElement.contentDocument.forms[2].children[0].value += 'boop'
};
z=''