Why Invoke Anonymous JavaScript Functions Immediately After Definition?

Why Invoke Anonymous Functions on the Same Line?

When working with closures, it's common to invoke an anonymous function on the same line it's defined. While this may seem arbitrary, it's essential for proper execution due to the way JavaScript handles function declarations.

Function Definition in JavaScript

JavaScript allows three methods for defining functions:

• Function Constructor: new Function('args', 'body')
• Function Declaration: function name(args) { body }
• Function Expression: var name = function(args) { body }

The key difference between declarations and expressions is that declarations require an identifier (name) while expressions can be anonymous.

Anonymous Functions and Line Breaks

Anonymous functions behave differently than named functions. When writing an anonymous function expression, you can optionally provide an identifier within the parentheses, but it's not necessary.

If you break the line after defining an anonymous function, JavaScript interprets it as a function declaration. However, since no identifier is provided, the declaration becomes invalid syntax.

Example:

This code creates an anonymous function expression and invokes it on the same line:

(function(msg) { alert(msg); })('Hello');

Invalid Example:

If you break the line and omit the parentheses, it becomes a malformed function declaration:

function(msg) { alert(msg); }

('Hello'); // Syntax error: Invalid function syntax without an identifier

To make it work, you need to add parentheses to invoke the anonymous function expression:

function(msg) { alert(msg); }('Hello');

Conclusion

Invoking anonymous functions on the same line ensures that they are properly executed as function expressions, preventing them from being misinterpreted as function declarations with missing identifiers.

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