Get list of items in one list that are not in another [closed]

Answer 1

If you are looking for the best possible way, this is what you have to do

1. Convert the list to be checked, to an object, in liner time. Because, objects are technically hashtables, which offer faster lookups O(1)).

2. Then, iterate over the first list and check if the current element is there in the object or not. If it is not there, add it to the result.

   var list1 = [1, 2, 3], list2 = [1, 2], dict2 = {};
   
   list2.forEach(function(item) {
       dict2[item] = true;
   });
   
   var result = list1.reduce(function(prev, current) {
       if (dict2.hasOwnProperty(current) === false) {
           prev.push(current);
       }
       return prev;
   }, [])
   
   
   console.log(result);
   

Output

[ 3 ]