Fastest way to comment out a block of code in vim

Given this code that you want to comment out

var someFunction = function(){
    some code I want
    to
    comment
    out
}

And your cursor is at the first {, you can type

1. v visual editor mode
2. % go to the matching }
3. :norm I// insert inline comments at the beginning of each line

// var someFunction = function(){
    // some code I want
    // to
    // comment
    // out 
// }