How is this valid javascript, and what purpose does it serve?

Question

I was answering a question on quora and encountered something like following:

// if(true)
{
   var qq = 1;
}

Immediately I fired up chrome and

Answer 1

The blocks are used just for statements like if(){}, function(){}, switch(){}, for(..){}, etc.

In this example:

var number = 0;
if(true)
    number = 1
else
    number = 2
    number = 3 //This line is evaluated because no longer is in the `else` condition

console.log(number); //3

Using blocks this will not happen:

var number = 0;
if(true)
{
    number = 1
}
else
{
    number = 2
    number = 3
}

console.log(number); //1

Using blocks without using any statement are unnecessary, eg:

var foo = 2;
foo = 3;
console.log(foo) //3

It is the same as doing:

var foo = 2;
{
    foo = 3;
}
console.log(foo) //3

Except if you are developing in an environment of ES6. Using let declarations in blocks are very important. And these will be evaluated only within the block.

let foo = 2;
{
    let foo = 3;
}

console.log(foo) //2