在回调中调用 function 与调用 function

Question

I want to understand how the getJSON function is invoked differently in the following two situations. What is getJSON if it is not a callback function, when I don't wrap it inside an arrow function?

First:

btn.addEventListener("click", ()=> {
  getJSON(astroURL);
})

Second:

btn.addEventListener("click", getJSON(astroURL))

Answer 1

The second argument to addEventListener is supposed to be the callback that is invoked each time the event occurs. Your first example is passing an arrow function as the callback, while your second example is passing the return value of getJSON(astroURL) to addEventListener , which is erroneous, unless the method itself returns a function.