How do you loop through an array and only extract key:value that are specific values?

Question

I would like to loop through an existing object and only extract specific keys to add to a new array.

The object looks like:

let lyricsData = {
   "success": true;
   "length": 50;
   "result": [
       {
         "id_track": 123,
         "haslyrics": true,
         "id_artrist": 234,
       },
       {
         "id_track": 567,
         "haslyrics": false,
         "id_artrist": 678,
    }
  ]
}

I would only like to extract the results if "haslyrics" is true .

This is the block of code I've come up with:

1  function findHasLyrics(lyricsData) {
2      if (lyricsData.length === 0) {
3          console.log("findHasLyrics", null);
4      } else {
5          let hasLyricsTrue = [];
6          for (let i=0; i<lyricsData.length; i++) {
7              if (lyricsData.result[i].haslyrics === true) {
8                  hasLyricsTrue.push(lyricsData.result[i]);
9              };
10             console.log("findHasLyrics", hasLyricsTrue);
11         };
12     };
13 };

Where is the code breaking? And how would I fix it?

Thanks in advance.

SOLUTION (EDITED). Thanks @StepUp and @Ankita.

I needed to keep the if-else statements. The lyricsData is dynamic and sometimes the length is 0. In that case, I need to pass a null through a function.

function findHasLyrics(lyricsData) {
    if (lyricsData.length === 0) {
        displayLyricsApi(null);
    } else {
        function findHasLyrics(lyricsData) {
            return lyricsData.result.filter(f => f.haslyrics)
    };
        formatQueryLyrics(findHasLyrics(lyricsData));
    };
}

Answer 1

Just use filter method:

lyricsData.result.filter(f=> f.haslyrics)

in your case:

function findHasLyrics(lyricsData) {
    return return lyricsData.result.filter(f=> f.haslyrics);
};

An example:

 var data = { "success": true, "length": 50, "result": [{ "id_track": 123, "haslyrics": true, "id_artrist": 234, }, { "id_track": 567, "haslyrics": false, "id_artrist": 678, } ] }; function findHasLyrics(lyricsData) { return lyricsData.result.filter(f=> f.haslyrics) }; console.log(findHasLyrics(data));

Answer 2

Just use Array.filter() to filter the array with those objects that has haslyrics value as true . You can avoid the custom loops and logic with that function.

 var obj = { "success": true, "length": 50, "result": [ { "id_track": 123, "haslyrics": true, "id_artrist": 234, }, { "id_track": 567, "haslyrics": false, "id_artrist": 678, } ] }; var res = obj.result.filter(({haslyrics}) => haslyrics); console.log(res);

In your code you can update this way:

 function findHasLyrics(lyricsData) { if (lyricsData.length === 0) { console.log("findHasLyrics", null); } else { var res = lyricsData.result.filter(({haslyrics}) => haslyrics); console.log(res); }; }; var obj = { "success": true, "length": 50, "result": [{ "id_track": 123, "haslyrics": true, "id_artrist": 234, }, { "id_track": 567, "haslyrics": false, "id_artrist": 678, } ] }; findHasLyrics(obj);

Answer 3

The problem is that you've made an easy to make mistake in the for signature, docs here .

The second argument you're using doesn't return an Integer (number), lyricsData.result is an array, you want to return its .length , ie:

for (let i=0; i<lyricsData.result.length; i++) {
  ...
}

However, I would advise you to use .filter as others have already suggested.