訪問和打印嵌套的 JSON object

Question

我無法訪問以下 object 中的嵌套鍵。 我正在嘗試在“close_approach_data”內的“relative_velocity”中打印所有“kilometers_per_second”。

我得到一個錯誤，不明白我做錯了什么。 先感謝您

const asteroidData = near_earth_objects
        .map((data) => data.close_approach_data[0])
        .map((e) => e.relative_velocity); 

// TypeError: Cannot read property 'relative_velocity' of undefined

or

const asteroidData = near_earth_objects
          .map((data) => data.close_approach_data[0].relative_velocity);

// TypeError: Cannot read property 'relative_velocity' of undefined

JSON object：

 "near_earth_objects": [
        {
            "links": {
                "self": "http://www.neowsapp.com/rest/v1/neo/2021277?api_key=24TE7EgNfmXIvdb6vNNZGBWx8s54XbZzCCi2oAdN"
            },
            "id": "2021277",
            "neo_reference_id": "2021277",
            "name": "21277 (1996 TO5)",
            "designation": "21277",
            "nasa_jpl_url": "http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2021277",
            "absolute_magnitude_h": 16.1,
            "estimated_diameter": {
                "kilometers": {
                    "estimated_diameter_min": 1.6016033798,
                    "estimated_diameter_max": 3.5812940302
                },
                "meters": {
                    "estimated_diameter_min": 1601.6033797856,
                    "estimated_diameter_max": 3581.2940301941
                },
                "miles": {
                    "estimated_diameter_min": 0.9951898937,
                    "estimated_diameter_max": 2.2253122528
                },
                "feet": {
                    "estimated_diameter_min": 5254.6044325359,
                    "estimated_diameter_max": 11749.652706022
                }
            },
            "is_potentially_hazardous_asteroid": false,
            "close_approach_data": [
                {
                    "close_approach_date": "1945-06-07",
                    "close_approach_date_full": "1945-Jun-07 22:35",
                    "epoch_date_close_approach": -775272300000,
                    "relative_velocity": {
                        "kilometers_per_second": "15.5094751879",
                        "kilometers_per_hour": "55834.1106763388",
                        "miles_per_hour": "34693.1450477507"
                    },
                    "miss_distance": {
                        "astronomical": "0.0334232973",
                        "lunar": "13.0016626497",
                        "kilometers": "5000054.084456751",
                        "miles": "3106889.5396991238"
                    },
                    "orbiting_body": "Mars"
                }
            ],
            "is_sentry_object": false
        },

       // Object continues repeating the above structure

Answer 1

您需要所有值還是只需要kilometers_per_second值？

 let near_earth_objects = [ { "links": { "self": "http://www.neowsapp.com/rest/v1/neo/2021277?api_key=24TE7EgNfmXIvdb6vNNZGBWx8s54XbZzCCi2oAdN" }, "id": "2021277", "neo_reference_id": "2021277", "name": "21277 (1996 TO5)", "designation": "21277", "nasa_jpl_url": "http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2021277", "absolute_magnitude_h": 16.1, "estimated_diameter": { "kilometers": { "estimated_diameter_min": 1.6016033798, "estimated_diameter_max": 3.5812940302 }, "meters": { "estimated_diameter_min": 1601.6033797856, "estimated_diameter_max": 3581.2940301941 }, "miles": { "estimated_diameter_min": 0.9951898937, "estimated_diameter_max": 2.2253122528 }, "feet": { "estimated_diameter_min": 5254.6044325359, "estimated_diameter_max": 11749.652706022 } }, "is_potentially_hazardous_asteroid": false, "close_approach_data": [ { "close_approach_date": "1945-06-07", "close_approach_date_full": "1945-Jun-07 22:35", "epoch_date_close_approach": -775272300000, "relative_velocity": { "kilometers_per_second": "15.5094751879", "kilometers_per_hour": "55834.1106763388", "miles_per_hour": "34693.1450477507" }, "miss_distance": { "astronomical": "0.0334232973", "lunar": "13.0016626497", "kilometers": "5000054.084456751", "miles": "3106889.5396991238" }, "orbiting_body": "Mars" } ], "is_sentry_object": false }]; let result = near_earth_objects.flatMap(({close_approach_data }) => close_approach_data.map(({relative_velocity})=> relative_velocity.kilometers_per_second)); console.log(result);

Answer 2

你的代碼很好，只需要轉換原始 json "near_earth_objects"

例子

const near_earth_objects = JSON.parse(JSON.stringify('YOUR_NEAR_EARTH')).near_earth_objects; 
const asteroidData = near_earth_objects
         .map((data) => data.close_approach_data[0].relative_velocity);

檢查這個

 const near_earth_objects_json = { "near_earth_objects": [ { "links": { "self": "http://www.neowsapp.com/rest/v1/neo/2021277?api_key=24TE7EgNfmXIvdb6vNNZGBWx8s54XbZzCCi2oAdN" }, "id": "2021277", "neo_reference_id": "2021277", "name": "21277 (1996 TO5)", "designation": "21277", "nasa_jpl_url": "http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2021277", "absolute_magnitude_h": 16.1, "estimated_diameter": { "kilometers": { "estimated_diameter_min": 1.6016033798, "estimated_diameter_max": 3.5812940302 }, "meters": { "estimated_diameter_min": 1601.6033797856, "estimated_diameter_max": 3581.2940301941 }, "miles": { "estimated_diameter_min": 0.9951898937, "estimated_diameter_max": 2.2253122528 }, "feet": { "estimated_diameter_min": 5254.6044325359, "estimated_diameter_max": 11749.652706022 } }, "is_potentially_hazardous_asteroid": false, "close_approach_data": [ { "close_approach_date": "1945-06-07", "close_approach_date_full": "1945-Jun-07 22:35", "epoch_date_close_approach": -775272300000, "relative_velocity": { "kilometers_per_second": "15.5094751879", "kilometers_per_hour": "55834.1106763388", "miles_per_hour": "34693.1450477507" }, "miss_distance": { "astronomical": "0.0334232973", "lunar": "13.0016626497", "kilometers": "5000054.084456751", "miles": "3106889.5396991238" }, "orbiting_body": "Mars" } ], "is_sentry_object": false }, { "links": { "self": "http://www.neowsapp.com/rest/v1/neo/2021277?api_key=24TE7EgNfmXIvdb6vNNZGBWx8s54XbZzCCi2oAdN" }, "id": "2021277", "neo_reference_id": "2021277", "name": "21277 (1996 TO5)", "designation": "21277", "nasa_jpl_url": "http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2021277", "absolute_magnitude_h": 16.1, "estimated_diameter": { "kilometers": { "estimated_diameter_min": 1.6016033798, "estimated_diameter_max": 3.5812940302 }, "meters": { "estimated_diameter_min": 1601.6033797856, "estimated_diameter_max": 3581.2940301941 }, "miles": { "estimated_diameter_min": 0.9951898937, "estimated_diameter_max": 2.2253122528 }, "feet": { "estimated_diameter_min": 5254.6044325359, "estimated_diameter_max": 11749.652706022 } }, "is_potentially_hazardous_asteroid": false, "close_approach_data": [ { "close_approach_date": "1945-06-07", "close_approach_date_full": "1945-Jun-07 22:35", "epoch_date_close_approach": -775272300000, "relative_velocity": { "kilometers_per_second": "15.5094751879", "kilometers_per_hour": "55834.1106763388", "miles_per_hour": "34693.1450477507" }, "miss_distance": { "astronomical": "0.0334232973", "lunar": "13.0016626497", "kilometers": "5000054.084456751", "miles": "3106889.5396991238" }, "orbiting_body": "Mars" } ], "is_sentry_object": false } ] } const near_earth_objects = JSON.parse(JSON.stringify(near_earth_objects_json)).near_earth_objects; const asteroidData = near_earth_objects.map((data) => data.close_approach_data[0].relative_velocity); console.log(asteroidData);

如果你只想要kilometers_per_second ，你可以這樣做

const asteroidData = near_earth_objects
          .map((data) => data.close_approach_data[0].relative_velocity.kilometers_per_second);