iFrame communication question

    window.parent.sendRequest(a+ "=", b, 50, function (response) {
      console.log(response);
    });[/code:3ui4xw25]

I try to make my own behaviour and its look like this
[code:3ui4xw25]Acts.prototype.sendRequest = function (a, b)
	{
		console.log(a);
		console.log(b);
		window.parent.sendRequest(a + "=", b , 0, function (response) {
			console.log(response);
			this.returnValue = response;
		});
	};[/code:3ui4xw25]

and its not work, and when i see inspect element they look like this

TypeError: window.parent.Fo is not a function

why I cant called the function name, and instead c2 call "fo" what is that 
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