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JavaScript Asynchronous Programming with JavaScript Asynchronous JavaScript with Callbacks Async Programming and Callback Functions

Hamzah Iqbal
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Hamzah Iqbal
Full Stack JavaScript Techdegree Student 11,145 Points

What is the purpose of the () => getJSON, as in why does it need the () ?

I understrøms that one is pasning in the function but what is the purpose of the ()

3 Answers

Steven Parker
Steven Parker
210,425 Points

The parentheses just act as a placeholder for when the function takes no arguments. They are also used when the function takes multiple arguments. The only case where they are not needed is when the function takes only one argument (in which case the parameter name would be there).

Hi Steven, thanks for your help. Can you clarify a little? I'm still confused.

not sure why it is: btn.addEventListener('click', () => getJSON(astrosUrl));

instead of btn.addEventListener('click', getJSON(astrosUrl));

why do you have to add the anonymous function () =>

Thank you so much!

Steven Parker
Steven Parker
210,425 Points

The anonymous function will run when the event occurs. It will run the "getJSON" at that time.

If you don't create the function, it will run "getJSON" now instead, plus it will expect it to return a function to be used as a callback when the event does happen.

i get it now!! Makes sense!! I really appreciate your expertise, thanks brother!!

Steven Parker
Steven Parker
210,425 Points

Rafic Jouejati — Glad to help. You can mark a question solved by choosing a "best answer".
And happy coding!

Farid Lavizadeh
Farid Lavizadeh
12,004 Points

Unless a named function is tied to an event, it will just run without the event occurring. Since getJSON(astrosUrl) is not tied to any event, it will run before a user clicks anything. To tie the named function to an event, a preceding anonymous function is used.