rummikub_regex.js

"1@23@@678@abc@".match(/(@*(\d|[abcd]){3,}@*)/g).join("").length === 13

testing: https://regex101.com/r/03qRen/1

const validateRunBoard = (board) => {
   for(i=0;i<board.length; i++){
      const row = board[i];
      if(!/@{13}/g.test(row)){
          // has cards on the row
          const isValid = row.match(/(@*(\d|[abcd]){3,}@*)/g).join("").length === 13;
          if(!isValid) return false;
      }
   }
   return true;
}

validateRunBoard(["@@@@@@@@@@@@@", "123456789abcd", "123@@678@abc@",  "@234@@789abcd", "@@@@@678@@@@@"]) // true
validateRunBoard(["@2@4567@9a@@@", "@2@4567@9abc@"]) // false

useful function

[true, true, false].every((i)=>i==true) // false