When Should I Use Parentheses in JavaScript `setTimeout` Function Calls?

When to Use Parentheses in Function Calls

In the provided code snippet:

var myFunction = function() {
   setTimeout(myFunction, 1000);
}
myFunction();

The function call within setTimeout does not require parentheses because setTimeout expects a function reference as an argument. myFunction references the function.

In contrast, myFunction() in the last line calls the function. When using the parentheses with myFunction, it invokes the function and executes its code.

Exception to the Rule

Under certain circumstances, setTimeout(myFunction(), 1000) might make sense. For instance, if myFunction() returns a function itself:

function myFunction() {
    return function() {
        alert("ohai")
    }
}

In this case, setTimeout(myFunction(), 1000) does the following:

• Calls the myFunction function, which returns the anonymous function that displays the alert.
• Sets the returned function as the argument to setTimeout.

As a result, an alert will be triggered every second.

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