I am asking this question because I and my colleague have a dispute on coding style because he prefers arrows function declaration:

const sum = (a, b) => a + b;

And I prefer old-style standalone function declaration:

function sum(a, b) {

    return a + b;

}

My point is that code in old-style more readable and you can more clearly distinguish function and variable declarations. His point is that code with arrow functions just run faster.

Do you know something about actual performance penalties (in v8) when you use old-style standalone function declaration instead of arrow functions? Are that penalties really exists?