Function References vs. Function Calls: When Do Parentheses Matter in JavaScript?

Function References vs Function Calls with Parentheses

In JavaScript, parentheses play a crucial role in distinguishing between referencing a function and actually calling it.

When we define a function using the function keyword, as in the example where myFunction is declared, the function itself is referenced without parentheses. This is because the declaration creates a function object in memory, and the variable myFunction holds that reference.

On the other hand, when we want to invoke a function, we use parentheses. In the last line of the given code, myFunction();, the parentheses indicate that we are calling the myFunction function immediately.

To understand the difference further, we can examine the setTimeout function. setTimeout expects a function reference as its first argument. By passing myFunction, we provide it with the reference to the function. This is why parentheses are not required in setTimeout(myFunction, 1000).

However, there are rare cases where using parentheses with setTimeout() can make sense. This is when your function returns another function. For instance, if myFunction returns a function that displays an alert every second, using parentheses in setTimeout(myFunction(), 1000) would cause multiple alerts to be triggered continuously.

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