How does determine whether the current frame is a Keyframe?

I wrote a simple command that needed to use an if statement to determine the condition. I checked the manual, but I couldn't find an example of judging keyframes.
The ideas are as follows:

//Select the current frame.
//Condition judgment:
if (if the current frame equals a Keyframe) {
//execute Command 1
} else {
//if the current frame is not a Keyframe, add a Keyframe and execute command 2
}

The stupid code I wrote can run, but will make an error in the first frame of the layer.
thank you very much!!