CODEWITHSUNDEEP
javascriptdom-events
Asad Seeker
Asad Seeker

Reputation: 67

Why we not use () while calling function in EventListener in JavaScript

I am new to JavaScript. I read a code which is: 

document.getElementById("myBtn").addEventListener("click", displayDate);
function displayDate() {
  document.getElementById("demo").innerHTML = Date();
}

I read the documentation, in this I get that the second parameter of addEventListener would be a function like the bellow (here after function we use () brackets)

document.getElementById("myBtn").addEventListener("click", function(){
document.getElementById("demo").innerHTML = Date();
});

according to my knowledge, we must use () after a function which is not in the first example. Even if I use than it doesn't work. So my question is why we can't use () if we create a separate function. I hope you understand my question.

Upvotes: 0

Views: 164

Answers (1)

Aplet123
Aplet123

Reputation: 35512

The parentheses mean different things in these scenarios. The parentheses that go after the function keyword denote a list of arguments that you provide to the function, e.g. function(a, b, c) signifies that the function takes 3 arguments, a, b, and c. The parentheses that go after displayDate represent the fact that you are calling the function with no parameters, and passing the return value to addEventListener. Since displayDate returns undefined, you are essentially setting undefined as an event listener, which will do nothing.

Upvotes: 3

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