[solved] look's like pre increment in while condition is skipping the first increment

Why do this two do while loops produce different output?

var dataLen4 = 4;
var idx = 0;
do {
      console.log("1. idx:", idx, idx << 2);
      ++idx;
} while(idx <  dataLen4 );
/* output
1. idx: 0 0
1. idx: 1 4
1. idx: 2 8
1. idx: 3 12
*/

idx=0;
do {
      console.log("2. idx:", idx, idx << 2);
} while(++idx <  dataLen4 );
/* output
2. idx: 0 0
2. idx: 2 8
2. idx: 3 12
*/

Code was running on a PICO_R1_3 with 2v06.49.