Local variable declaration style

Questions
1

Hello,

I have a question about the style of local variable declaration.

The usual way is as follows:

(
var a1, a2, a3, a4;
a1 = 1;
a2 = 2;
a3 = 3;
a4 = 4;
the rest of the code block
)

The following style as well:

(
var a1=1, a2=2, a3, a4;
a3 = 3;
a4 = 4;
the rest of the code block
)

Many users also write as follows:

(
var a1 = 1;
var a2 = 2;
var a3 = 3;
var a4 = 4;
the rest of code block
)

I sometimes write as follows to reduce typing:

(
var 
a1 = 1,
a2 = 2,
a3 = 3,
a4 = 4;

the rest of the code block
)

I think it is practical in many cases, but it may not be so beautiful.

My question is as follows:

  • if there would be problems with this style;
  • why this style is commonly not used.

Thanks!