How to prevent multiple decimals in JS calculator?

I have moved the individual button functions so that they are all under a main button click function.

I need to re-write my code pertaining to the decimal button so that not only can someone only press one decimal at a time, but can press the decimal again for a different number in the same equation. For example: 3.2 + 3.2. Right now, I have it written so that once you push the decimal, it is disabled. So only one number could have a decimal until you refresh the page.

My pseudo code would be:

If button clicked is decimal {
If decimal clicked, only allow one decimal unless an operand button ( +, -, x, /) is clicked afterwards.
If an operand is clicked and then another number, the decimal button may be clicked again, once only.
}
When the = button is clicked, reset keysPressed to " ".

How do I translate that into actual JS? Or is that oversimplified?