Iterate through Nested Array in JavaScript

Question

I'm trying to Iterate through a nested array and having trouble extracting the correct value.

My 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
        }
    ]
},

I would like to extract only the Key name from the Regions Array into an Array.

MY code which works fine and gives me the output:

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)
    }
}

Output

AMSTERDAM
AMSTERDAM03
CHENNAI

I would like to know if there a faster way to iterate rather than running it into two for loops??

Thank you

Answer 1

You can use Array.flatMap() (not supported in IE/Edge) with 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) 

If you can't use Array.flatMap() you can use an external Array.map() and spread the results into Array.concat() instead:

 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

You can use .map() and destructuring assignment

 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

Another solution for this is using 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

Well its pretty much the same thing but using a forEach method or array type in javascript can save you some time. here is an example.

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

a forEach executes an anonymous function passing each element in array as the argument to the anonymous function