Set variable in parent window from iframe

Variables in the global scope are auto-exposed as DOM properties of their containing window object.

This means that

var foo = 'bar';

is analogous to = 'bar';

Which means that you can read the global scope of any window object you can obtain a reference to. What we can also imply here is that usage of window is implicit. Even when you don’t explicitly type “window.”, it’s there anyway.

And since frames themselves are also auto-exposed as DOM properties of the current window object, this means you can access any other frames’ window object as well.

The parent property of window objects holds a reference the window object of that window’s parent (if there is one). Since iframes most certainly have a parent window, then all this stuff I just typed boils down to this

// set the global variable 'foo' in the parent global scope = 'bar';

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