empty array element require elision=true

with this a partially fill array, the web ide send me a message about elision.
what i'm suppose to do?
i do not understand the message!
i do not want to fill the array, if it's empty, it's "undefined", i test it and do something if it true or not...

Would you explain goo doesn't answer to me :/ (sorry)
do i have to change something, because it seems to work on the espruino!

thanks for your help

const lL = [,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,2,2,,4,,,,0,4,4,,5,,3,2,4,0,1,,,,,,,,,2,2,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,4,,4,,,,4,4,3,3,3,3,5,5,2,3,4,3,6,4,3,6,4,5,3,3,3,4,5,4,5,4,,,,,,,2,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,4,,4,,,,,3,3,3,3,3,,,2,2,,,,,3,,3,,,3,,3,3,,,2];
for (const l of lL) {
  if (l == undefined) {
    console.log("vide");
  } else {
    console.log(l);
  }
}