function merge_array(array1, array2) {  
    var result_array = [];  
    var arr = array1.concat(array2);  
    var len = arr.length;  
    var assoc = {};  
  
    while(len--) {  
        var item = arr[len];  
  
        if(!assoc[item])   
        {   
            result_array.unshift(item);  
            assoc[item] = true;  
        }  
    }  
  
    return result_array;  
}  
  
  
var array1 = [1, 2, 3];  
  
var array2 = [2, 30, 1];  
  
console.log(merge_array(array1, array2));  