first =  function(array, n) {  
      if (array == null)   
      return void 0;  
    if (n == null)   
      return array[0];  
    if (n < 0)  
      return [];  
    return array.slice(0, n);  
  };  
  
console.log(first([7, 9, 0, -2]));  
console.log(first([],3));  
console.log(first([7, 9, 0, -2],3));  
console.log(first([7, 9, 0, -2],6));  
console.log(first([7, 9, 0, -2],-3));