for..in vs for..v

var testObj = {
    'test' : '1',
    'test2' : '2'
};

for( var v in testObj ){
    console.log( v );
    console.log( testObj[v] );
}

console.log( "=======" );

var testArr = [ '1', '2', '3', '4' ];

for(  var v of testArr ){
    console.log( v );
}