Is There a Functional Difference Between `})()` and `}());` in JavaScript?

Function Invocation Syntax in JavaScript: Exploring the Nuances

In JavaScript, the syntax for invoking functions can vary, leading to questions about their functional equivalence. Consider the following two code blocks:

(function() {
    bar = 'bar';
    alert('foo');
})();

alert(bar);

(function() {
    bar = 'bar';
    alert('foo');
}());

alert(bar);

Both code blocks successfully alert "foo" and then "bar". The only noticeable difference seems to be the use of })() and }()); at the end. So, is there any functional distinction between these two approaches?

Identical Functionality

In this particular scenario, no functional difference exists between the two syntaxes. Both forms execute the code within the anonymous function, assigning the value 'bar' to the variable bar and displaying the alert messages as intended. Therefore, they are functionally equivalent.

When Differences Arise

However, there are situations where the two syntaxes produce different outcomes. Consider the following modifications:

new (function() {
    this.prop = 4;
})().prop;

new ( function() {
    return { Class: function() { } }; 
}() ).Class;

In the first code block, new is used to create a new instance of a class, and the prop property of that instance is accessed. This returns the value 4.

In contrast, the second code block calls new on the Class property of an object returned by a function. Since the parentheses surrounding the function call are within the outer parentheses, they do not trigger new but rather execute the function normally. Thus, the Class property is instantiated instead.

Conclusion

In most cases, })() and }()); are interchangeable for invoking functions without any functional implications. However, if new is used prior to the parentheses or operations are performed after the parentheses, the syntax may affect the code's behavior. It is crucial to be aware of these nuances to write JavaScript code that functions as intended.

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