Using hasOwnProperty for nested object keys if key name is a number

Question

I'm currently building a Pokémon application, therefor I'm accessing data from PokéAPI and will store specific data in a variable, such as name, id and type.

Currently I'm facing issues to store the second type of a pokémon. Some of them have one type, some of them have two.

If a pokémon has two types the data structure looks like this: Bulbasaur JSON data screenshot from pokeapi.co/api/v2/pokemon/bulbasaur

Here's the link to JSON data for an example pokémon with 1 types: https://pokeapi.co/api/v2/pokemon/bulbasaur

If a pokémon only has one type the structure looks like this: Togepi JSON data screenshot from https://pokeapi.co/api/v2/pokemon/togepi

Link: https://pokeapi.co/api/v2/pokemon/togepi

To check whether there's a second type or not I wrote a function:

function CheckPropertySecondtype(str) {
  if (str.hasOwnProperty("types"[1])) {
    pokemondata.secondtype = str.types[1].type.name;
    console.log("Pokemon has a second type");
  } else {
    pokemondata.secondtype = "none";
    console.log(str.types[1].type.name);
  }
}

The problem is, that the if statement doesn't work the way I want it to. It's always false which means no matter if there's a second type or not, the output is always "none". I tried several notations like hasOwnProperty(types[1].type.name) or hasOwnProperty(types1.type.name).

How can I access the key correctly to check this?

"types"[1] is the string "y", so str.hasOwnProperty("types"[1]) is equivalent to str.hasOwnProperty("y") — Barmar
– Barmar, Commented Oct 11, 2024 at 15:52
This looks like a job for optional chaining: str?.types?.[1] — Barmar
– Barmar, Commented Oct 11, 2024 at 15:55
"Here's the link to JSON data for an example pokémon with 1 types:": I see a structure that has 2 types? Is this a typo? — trincot
– trincot, Commented Oct 11, 2024 at 16:10
Thanks for taking a look at my issue! When I'm absolutely sure that the syntax must be str.types[1].type.name I shouldn't need optional chaining, right? I just don't know how to write str.types[1].type.name as prop in .hasOwnProperty() when str.hasOwnProperty(types[1].type.name) is impossible — Ameh
– Ameh, Commented Oct 11, 2024 at 16:11
@trincot yes, that was a typo (and I can't correct it, too late) — Ameh
– Ameh, Commented Oct 11, 2024 at 16:12

trincot · Accepted Answer · 2024-10-11 16:27:17Z

1

You don't need the if...else construct here. With the operators ?. (optional chaining) and ?? (nullish coalescing), you can do it in a single assignment:

pokemondata.secondtype = str.types[1]?.type?.name ?? "none";

This works because the name property is assumed to be a string, and so if str.types[1]?.type?.name is undefined, we know for sure it wasn't present, and so the ?? expression will evaluate to "none".

answered Oct 11, 2024 at 16:27

trincot

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1 Comment

Bergi Over a year ago

You may need only str.types[1]?.type.name even (with a single optional chaining operator)

Pufferfish101007 · Accepted Answer · 2024-10-11 16:10:41Z

1

As others have mentioned in the comments, str.hasOwnProperty("types"[1])is equivalent to str.hasOwnProperty("y"), which should be false. One option is to split it into two conditions:

if (str.hasOwnProperty("types") && str.types.hasOwnProperty(1)) {
 // ...
}

(note that the second condition could be rewritten as str.types.length >= 1). If str does not have a types property, the expression will short circuit and so the check for str.types[1] will never run (so won't error).

Or, you could write it more simply using optional chaining:

if (str.types?.[0] !== undefined) {
 // ..
}

answered Oct 11, 2024 at 16:10

Pufferfish101007

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Comments

Haluk · Accepted Answer · 2024-10-11 18:17:19Z

As an alternative, you can check the length of types in the JSON.

// shortened JSON data for the first URL:       
        var strJSON1= '{"types": [{"slot": 1, "type": {"name": "fairy", "url": "https://pokeapi.co/api/v2/type/18/"}}]}' ;

        var data= JSON.parse(strJSON1);
        console.log("*****URL-1******");

        console.log('Count of types: ' + data.types.length);

        for (var i=0; i<data.types.length; i++){
            console.log("Name" + (i+1) +": " + data.types[i].type.name);
        }

// Last name encountered:        
        console.log("Last Name found: " + data.types[data.types.length-1].type.name);


// shortened JSON data for the second URL:
        var strJSON2= '{"types": [{"slot": 1,"type": {"name": "grass","url": "https://pokeapi.co/api/v2/type/12/"}},{"slot": 2,"type": {"name": "poison","url": "https://pokeapi.co/api/v2/type/4/"}}]}' ;
 
        var data= JSON.parse(strJSON2);

        console.log("*****URL-2******");


        console.log('Count of types: ' + data.types.length); 
        for (var i=0; i<data.types.length; i++){
            console.log("Name" + (i+1) +": " + data.types[i].type.name);
        }
 
// Last name encountered:        
        console.log("Last Name found: " + data.types[data.types.length-1].type.name);

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