Difference and intersection of two arrays containing objects

Question

I have two arrays list1 and list2 which have objects with some properties; userId is the Id or unique property:

list1          


        

Answer 1

Use lodash's _.isEqual method. Specifically:

list1.reduce(function(prev, curr){
  !list2.some(function(obj){
    return _.isEqual(obj, curr)
  }) ? prev.push(curr): false;
  return prev
}, []);

Above gives you the equivalent of A given !B (in SQL terms, A LEFT OUTER JOIN B). You can move the code around the code to get what you want!