var var1 = 1, var2 = 1, var3 = 1;
In this case var keyword is applicable to all the three variables.
var var1 = 1,
var2 = 1,
var3 = 1;
which is not equivalent to this:
var var1 = var2 = var3 = 1;
In this case behind the screens var keyword is only applicable to var1 due to variable hoisting and rest of the expression is evaluated normally so the variables var2, var3 are becoming globals
Javascript treats this code in this order:
/*
var 1 is local to the particular scope because of var keyword
var2 and var3 will become globals because they've used without var keyword
*/
var var1; //only variable declarations will be hoisted.
var1= var2= var3 = 1;