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In JavaScript, function expressions without parentheses can resemble function declarations, leading to syntax errors. To resolve this ambiguity, the plus sign (or other unary operators) can be used as a prefix to enforce the interpretation of the following expression as a function expression.
Consider the following code:
+function(){console.log("Something.")}()
Without the plus sign, the JavaScript parser would consider this as a function declaration, which requires a name. Adding the plus sign forces the parser to treat the subsequent expression as a function expression, allowing for immediate invocation.
Using the plus sign prefix offers the following advantages:
Parentheses can also be used to enclose the function expression, providing an alternative approach:
(function() { console.log("Foo!"); })();
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