Invoking a function without parentheses

I was told today that it's possible to invoke a function without parentheses. The only ways I could think of was using functions like apply or call. f.apply(this); f.call(this); But these require parentheses on apply and call leaving us at square one. I also considered the idea of passing the function to some sort of event handler such as setTimeout: setTimeout(f, 500); But then the question becom

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括弧を使わないで関数を呼ぶ方法