Data filtering Javascript (Nested dictionary and arrays)

Question

I`m trying to figure out how js filter() works.

I have an API, which returns something like this:

[
    {
        "name": "Category 1",
        "items": [
            {
                "name": "Vacancy item #1",
                "location": "Los Angeles",
                "overview": "Lorem ipsum",
                "get_absolute_url": "/careers/vacancy-item-1/"
            },
            {
                "name": "Vacancy item #2",
                "location": "Los Angeles",
                "overview": "Lorem ipsum",
                "get_absolute_url": "/careers/vacancy-item-2/"
            }
        ]
    },
    {
        "name": "Category 2",
        "items": [
            {
                "name": "Vacancy item #3",
                "location": "Washington D.C",
                "overview": "Lorem ipsum",
                "get_absolute_url": "/careers/vacancy-item-3/"
            }
        ]
    }
]

I want to filter this data based on the select value of the form. I`m working on the VUE.JS and Django.

And this is my JS code

filteredItems() {
                let vacancycategories = this.listData,
                    city = this.city,
                    category = this.category


                if (city && city.length > 0) {
                    vacancycategories = vacancycategories.filter((cat) => {

                         cat.items = cat.items.filter((vacancy) => {
                            return vacancy.location.indexOf(city) !== -1
                        })
                            return cat
                    })
                } 

                if (category && category.length > 0) {
                    vacancycategories = vacancycategories.filter((cat) => {
                        return cat.name.indexOf(category) !== -1
                    })
                }  
                return vacancycategories
            }

The category part is working as expected. But when I try to filter location fields, it's not working properly. The first selected option works normal but then when you select another option it returns an empty list.

Answer 1

every filter function need to return the boolean value.
Inner filter function is fine, But the outer filter function need to change. Following changes should work.

vacancycategories = vacancycategories.filter(cat => {
  return (
    cat.items.filter(vacancy => {
      return vacancy.location.indexOf(city) !== -1;
    }).length > 0
  );
});