Vanilla Javascript filter function works perfect in one line, but not work at all for other-CodePudding

I am trying to filter JSON file with plain JavaScript.

city = await cities.filter(ea => {
    return ea.city.toLowerCase().includes(searcher.value.toLowerCase()); //example value Belgrade
});

admin = await cities.filter(eb => {
    return eb.admin_name.toLowerCase().includes(searcher.value.toLowerCase()); //example value Beograd
});

While filter that goes to city variable works perfect, one that goes to admin variable, witch is Copy-Paste of first one, return error:

Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'toLowerCase')

and even if I remove toLowerCase function I get same error but (reading 'includes')

this is structure of JSON file:

[
 {
  "city": "Tokyo",
  "city_ascii": "Tokyo",
  "lat": 35.6839,
  "lng": 139.7744,
  "country": "Japan",
  "iso2": "JP",
  "iso3": "JPN",
  "admin_name": "Tōkyō",
  "capital": "primary",
  "population": 39105000,
  "id": 1392685764
 },
]

CodePudding user response：

That just means admin_name doesn't exist, or is null/undefined for at least one object of your array.

In order to support this, you could use optional chaining like this:

admin = cities.filter(eb => {
    return eb.admin_name?.toLowerCase()?.includes(searcher.value.toLowerCase()); //example value Beograd
});

As a side note, awaiting a non Promise value just returns that value, so it's useless in your case.