Why do we use a plus sign in front of function name in JavaScript?

The +function() {} notation is primarily used to force the parser to treat whatever follows the + as an expression. This is commonly used for Immediately Invoked Function Expressions (IIFEs).

The Problem Without +

Without the plus sign, JavaScript interprets a function declaration, which cannot be immediately invoked:

// This causes a syntax error
function() { console.log("Demo!"); }();

Using + to Create an IIFE

The + operator converts the function declaration into an expression, allowing immediate invocation:

Alternative Operators

You can use other unary operators like !, -, or ~ to achieve the same result:

Using Parentheses (Most Common)

Parentheses are the most popular and readable way to create IIFEs:

Comparison

Conclusion

The + sign forces function declarations to become expressions for immediate invocation. However, parentheses are preferred for better readability and convention in modern JavaScript.