Is var necessary when declaring Javascript variables? [duplicate]

Answer 1

From http://www.updrift.com/article/to-var-or-not-to-var-my-javascript

1. For global variables, it doesn’t matter, but you may want to use it for consistency.
2. Always try to use ‘var’ to declare variables in local functions. It makes sure you’re using a local copy of the variable instead of another variable of the same name in a different scope.

For example, the two similar functions here have very different effects:

var myvar = 0;
function affectsGlobalVar(i){
   myvar = i;
}
function doesNotAffectGlobalVar(i){
   var myvar = i;
}