Assigning event handler

Question

Assigning event handler like so:

document.addEventListener("DOMContentLoaded", myFunction);

is it required for the handler function to be defined before the assignment code? In other words if the codes below

function myFunction() {...}
...
document.addEventListener("DOMContentLoaded", myFunction);

and

document.addEventListener("DOMContentLoaded", myFunction);
...
function myFunction() {...}

are identical?

well.. did you try it for yourself...? What did you find...? — Sudhir Bastakoti
– Sudhir Bastakoti, Commented Sep 18, 2017 at 10:10
@SudhirBastakoti: Trying it can be useful, but only tells you whether it works on the JavaScript engine(s) where you tried it, as opposed to whether it's supposed to work. — T.J. Crowder
– T.J. Crowder, Commented Sep 18, 2017 at 10:10
function declaration is hoisted which means it is evaluated before any other code in current context.. — Rayon
– Rayon, Commented Sep 18, 2017 at 10:11

T.J. Crowder · Accepted Answer · 2017-09-18 10:10:08Z

2

...are identical?

They are if you use the form you've shown, which is a function declaration. Function declarations are processed before any step-by-step code in the scope. If you used a function expression instead (var myFunction = function() { ... };), it would have to be before the addEventListener call. More about the difference in this question's answers.

answered Sep 18, 2017 at 10:10

T.J. Crowder

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