Call a function from iframe to parent and vice versa

//The following code calls the function that exists in the main window from the iframe window
if(typeof parent.window !== 'undefined' && typeof parent.window.functionName === 'function'){
    parent.window.functionName(); //Call the function only if it exists
}

//The following code calls the function that exists in the iframe window from the main window
if(typeof document.frames['iframeName'] !== 'undefined' && typeof document.frames['iframeName'].functionName === 'function'){
    document.frames['iframeName'].functionName(); //Call the function available in the iframe window from the parent window.
}