在JavaScript中迭代嵌套數組

Question

我試圖通過嵌套數組迭代，無法提取正確的值。

我的Json FIle

var regions = [
{
    "id": 265592,
    "longName": "Amsterdam 1",
    "name": "ams01",
    "statusId": 2,
    "regions": [
        {
            "description": "AMS01 - Amsterdam",
            "keyname": "AMSTERDAM",
            "sortOrder": 0
        }
    ]
},
{
    "id": 814994,
    "longName": "Amsterdam 3",
    "name": "ams03",
    "statusId": 2,
    "regions": [
        {
            "description": "AMS03 - Amsterdam",
            "keyname": "AMSTERDAM03",
            "sortOrder": 26
        }
    ]
},
{
    "id": 1004997,
    "longName": "Chennai 1",
    "name": "che01",
    "statusId": 2,
    "regions": [
        {
            "description": "CHE01 - Chennai ",
            "keyname": "CHENNAI",
            "sortOrder": 30
        }
    ]
},

我想只將區域數組中的密鑰名稱提取到數組中。

我的代碼工作正常，並給我輸出：

const regions3 = []
for (let i = 0; i < regions.length; i++) {
    const element = regions[i]; 
    const regions1 = (element.regions)
    for (let j = 0; j < regions1.length; j++) {
        const element1 = regions1[j];
        const element2 = element1.keyname;
        regions3.push(element2)
        console.log(regions3)
    }
}

產量

AMSTERDAM
AMSTERDAM03
CHENNAI

我想知道是否有更快的迭代方式而不是將其運行為兩個for循環？

謝謝

Answer 1

您可以在Array.flatMap()使用Array.flatMap() （在IE / Edge中不支持Array.map() ：

 const regions = [{"id":265592,"longName":"Amsterdam 1","name":"ams01","statusId":2,"regions":[{"description":"AMS01 - Amsterdam","keyname":"AMSTERDAM","sortOrder":0}]},{"id":814994,"longName":"Amsterdam 3","name":"ams03","statusId":2,"regions":[{"description":"AMS03 - Amsterdam","keyname":"AMSTERDAM03","sortOrder":26}]},{"id":1004997,"longName":"Chennai 1","name":"che01","statusId":2,"regions":[{"description":"CHE01 - Chennai ","keyname":"CHENNAI","sortOrder":30}]}] const result = regions.flatMap(o => o.regions.map(p => p.keyname) ) console.log(result) 

如果你不能使用Array.flatMap()你可以使用外部Array.map()並將結果傳播到Array.concat() ：

 const regions = [{"id":265592,"longName":"Amsterdam 1","name":"ams01","statusId":2,"regions":[{"description":"AMS01 - Amsterdam","keyname":"AMSTERDAM","sortOrder":0}]},{"id":814994,"longName":"Amsterdam 3","name":"ams03","statusId":2,"regions":[{"description":"AMS03 - Amsterdam","keyname":"AMSTERDAM03","sortOrder":26}]},{"id":1004997,"longName":"Chennai 1","name":"che01","statusId":2,"regions":[{"description":"CHE01 - Chennai ","keyname":"CHENNAI","sortOrder":30}]}] const result = [].concat(...regions.map(o => o.regions.map(p => p.keyname) )) console.log(result) 

Answer 2

您可以使用.map()和解構賦值

 var regions = [{"id":265592,"longName":"Amsterdam 1","name":"ams01","statusId":2,"regions":[{"description":"AMS01 - Amsterdam","keyname":"AMSTERDAM","sortOrder":0}]},{"id":814994,"longName":"Amsterdam 3","name":"ams03","statusId":2,"regions":[{"description":"AMS03 - Amsterdam","keyname":"AMSTERDAM03","sortOrder":26}]},{"id":1004997,"longName":"Chennai 1","name":"che01","statusId":2,"regions":[{"description":"CHE01 - Chennai ","keyname":"CHENNAI","sortOrder":30}]}]; let res = regions.map(({regions: [{keyname}]}) => keyname); console.log(res); 

Answer 3

另一個解決方案是使用Array :: reduce（） ：

 var regions = [{"id":265592,"longName":"Amsterdam1","name":"ams01","statusId":2,"regions":[{"description":"AMS01-Amsterdam","keyname":"AMSTERDAM","sortOrder":0}]},{"id":814994,"longName":"Amsterdam3","name":"ams03","statusId":2,"regions":[{"description":"AMS03-Amsterdam","keyname":"AMSTERDAM03","sortOrder":26}]},{"id":1004997,"longName":"Chennai1","name":"che01","statusId":2,"regions":[{"description":"CHE01-Chennai","keyname":"CHENNAI","sortOrder":30}]}]; let res = regions.reduce( (acc, curr) => (curr.regions.forEach(x => acc.push(x.keyname)), acc), [] ); console.log(res); 

Answer 4

好吧它幾乎是一樣的但是在javascript中使用forEach方法或數組類型可以節省你一些時間。 這是一個例子。

const regions3 = [];
        regions.forEach(function(region){
            region.regions.forEach(function(subRegion){
                regions3.push(subRegion.keyname);
                console.log(subRegion.keyname);
            })
        });

forEach執行一個匿名函數，將數組中的每個元素作為匿名函數的參數傳遞