example.js

// Example using function
alert(joinSeparated(['test','+','test'],'+'));

joinSeperated.js

// The function, copy and paste this
function joinSeparated(array, separator) {
  for (i in array){
      try {
        i--;
        if (array[i]==separator){
          array[i]=array[i-1]+array[i]+array[i+1];
          array.splice(i+1,1);
          array.splice(i-1,1);
        }
      } catch (err) {
        console.log('Joiner error:' + err)
      }
  }

  return array;
}