Javascript create a new array from a nested structure

Question

I have the below JSON;

"level1":[
    {
        "id":"0",
        "index":"0",
        "label":"Level 1 Label a",
        "level2":[
            {
            "id":"0",
            "index":"0",
            "label":"Level 2 Label 1a",
            "level3":[
                {"id":"UniqueId1","index":"0","label":"Level 3 Label 00a"}
            ]
            },
            {
            "id":"1",
            "index":"1",
            "label":"Level 2 Label 1b",
            "level3":[
                {"id":"UniqueId2","index":"0","label":"Level 3 Label 00b"}
            ]
        }]
    },
    {
        "id":"1",
        "index":"1",
        "label":"Level 1 Label b",
        "level2":[
            {
            "id":"0",
            "index":"0",
            "label":"Level 2 Label 2a",
            "level3":[
                {"id":"UniqueId3","index":"0","label":"Level 3 Label a"}
            ]
            },
            {
            "id":"1",
            "index":"1",
            "label":"Level 22 Label",
            "level3":[
                {"id":"UniqueId4","index":"0","label":"Level 3 Label b"}
            ]
        }]
    }
]

My question is if there is a way to create an array of all strings from this of level3.id So given this input, I want the output to be

["UniqueId1", "UniqueId2", "UniqueId3", "UniqueId4"]

I am thinking of using map...but not sure if there is a better way.

Alireza Ahmadi · Accepted Answer · 2021-09-28 06:34:06Z

2

The simplest way is using flatMap like this:

level1 = [
        {
            "id": "0",
            "index": "0",
            "label": "Level 1 Label a",
            "level2": [
                {
                    "id": "0",
                    "index": "0",
                    "label": "Level 2 Label 1a",
                    "level3": [
                        { "id": "UniqueId1", "index": "0", "label": "Level 3 Label 00a" }
                    ]
                },
                {
                    "id": "1",
                    "index": "1",
                    "label": "Level 2 Label 1b",
                    "level3": [
                        { "id": "UniqueId2", "index": "0", "label": "Level 3 Label 00b" }
                    ]
                }]
        },
        {
            "id": "1",
            "index": "1",
            "label": "Level 1 Label b",
            "level2": [
                {
                    "id": "0",
                    "index": "0",
                    "label": "Level 2 Label 2a",
                    "level3": [
                        { "id": "UniqueId3", "index": "0", "label": "Level 3 Label a" }
                    ]
                },
                {
                    "id": "1",
                    "index": "1",
                    "label": "Level 22 Label",
                    "level3": [
                        { "id": "UniqueId4", "index": "0", "label": "Level 3 Label b" }
                    ]
                }]
        }
    ]


console.log( level1.flatMap(t=>t.level2).flatMap(t=>t.level3).map(x=>x.id))

answered Sep 28, 2021 at 6:34

Alireza Ahmadi

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2 Comments

copenndthagen Over a year ago

Thanks...I am really not aware of flatMap...How is the modern browser support for this ?

Alireza Ahmadi Over a year ago

@copenndthagen You're welcome. The flatMap() method returns a new array formed by applying a given callback function to each element of the array, and then flattening the result by one level. So when you need to go for two level you need to use them twice and then you can get any property you want

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