flatten.js

const flatten = filter => {
    const filters = filter.filters;
    if (filters) {
        return filters.reduce((acc, curr) => acc.concat(curr.filters ? flatten(curr) : [curr]), []);
    }
    return [];
};

const rootFilters = {
  filters: [
    { 
      filters: [{ value: 'test1' }] 
    },
    { 
      filters: [
        { 
          filters: [{ value: 'test2' }] 
        }
      ]
    }        
  ]
};

flatten(rootFilters);