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javascript - 访问和打印嵌套的 JSON 对象

问题描述

我无法访问以下对象中的嵌套键。我正在尝试在“close_approach_data”内的“relative_velocity”中打印所有“kilometers_per_second”。

我得到一个错误，不明白我做错了什么。先感谢您

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对象：

 "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

标签： javascriptjson

解决方案

您需要所有值还是只需要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);

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