Iterate through an array of objects Nodejs

Question

Need some help with this, been stuck for hours.

Trying to iterate through an array of objects in node to grab one of the key's value and perform a regex function.

I keep getting undefined reading errors, the latest one is

Cannot read properties of undefined (reading 'split')

The array is created by calling toArray() on a MongoDB collection find function:

"ups": [
  {
    "_id": "61b5ef3a8bec102408f5289e",
    "article_code": "4325832",
    "order_number": "",
    "status": "shipped",
    "tt_url": "https://www.ups.com/track?loc=en_US&tracknum=999&requester=ST/trackdetails",
    "unique_id": ""
  },
  {
    "_id": "61b5ef3a8bec102408f528b4",
    "article_code": "6242665",
    "order_number": "",
    "status": "shipped",
    "tt_url": "https://www.ups.com/track?loc=en_US&tracknum=999&requester=ST/trackdetails",
    "unique_id": ""
  },
  {
    "_id": "61b5ef3a8bec102408f528ef",
    "article_code": "3610890",
    "order_number": "",
    "status": "shipped",
    "tt_url": "https://www.ups.com/track?loc=en_US&tracknum=999&requester=ST/trackdetails",
    "unique_id": ""
  }
]

Here's my code attempt:

for(let i = 0; i < ups.length; i++) {       
    var ups_tt = i['tt_url'];
    var unique_id = i['unique_id'];
        
    var spl = ups_tt.split(/tracknum=(.*)/)[1];
    ups_tt = spl.split("&")[0];
}

Any help would be appreciated.

Answer 1

so, in your example, i is just a number, so if you try to get a key of a number, then you will get undefined

> let i = 1;
undefined
> i["test"]
undefined

what you should do is reference the array ups with the index:

 for(let i = 0; i < ups.length; i++){
       
        var ups_tt = ups[i].tt_url;
        var unique_id = ups[i].unique_id;
        
        var spl = ups_tt.split(/tracknum=(.*)/)[1];
        ups_tt = spl.split("&")[0];

Answer 2

Try this way:

let y = {
  "ups": [
    {
      "_id": "61b5ef3a8bec102408f5289e",
      "article_code": "4325832",
      "order_number": "",
      "status": "shipped",
      "tt_url": "https://www.ups.com/track?loc=en_US&tracknum=999&requester=ST/trackdetails",
      "unique_id": ""
    }, {
      "_id": "61b5ef3a8bec102408f528b4",
      "article_code": "6242665",
      "order_number": "",
      "status": "shipped",
      "tt_url": "https://www.ups.com/track?loc=en_US&tracknum=999&requester=ST/trackdetails",
      "unique_id": ""
    }, {
      "_id": "61b5ef3a8bec102408f528ef",
      "article_code": "3610890",
      "order_number": "",
      "status": "shipped",
      "tt_url": "https://www.ups.com/track?loc=en_US&tracknum=999&requester=ST/trackdetails",
      "unique_id": ""
    }
  ]
}
    
y.ups.forEach(element => {
  console.log(element)
});

Answer 3

since the url is simple enough, you can just directly split it by "&", no need to use regex

so:

ups_tt = ups_tt.split('&')[2];
var spl = "&" + ups_tt;

Answer 4

The error is on row var spl = ups_tt.split(/tracknum=(.*)/)[1]; , because ups_tt is undefined.

 for(let i = 0; i < ups.length; i++){ var ups_tt = i['tt_url']; var unique_id = i['unique_id']; var spl = ups_tt.split(/tracknum=(.*)/)[1]; ups_tt = spl.split("&")[0];

i is the index so it's a number. You could fix it adding either let elem = ups[i] inside the loop, or changing i[property] to ups[i][property] :

for(let i = 0; i < ups.length; i++){
    // A
    let elem = ups[i];
    var ups_tt = elem['tt_url'];
    var unique_id = elem['unique_id'];

    // B
    var ups_tt = ups[i]['tt_url'];
    var unique_id = ups[i]['unique_id'];

    // rest of the loop

Also, since you're also asking how to iterate an array of objects, you could use for .. of , built exactly to do that:

The for...of statement creates a loop iterating over iterable objects, including: built-in String, Array, array-like objects (eg, arguments or NodeList), TypedArray, Map, Set, and user-defined iterables. It invokes a custom iteration hook with statements to be executed for the value of each distinct property of the object.

Your code would look like this:

for (let elem of ups) {
    var ups_tt = elem['tt_url'];
    var unique_id = elem['unique_id'];

    var spl = ups_tt.split(/tracknum=(.*)/)[1];
    ups_tt = spl.split("&")[0];

    // rest of the loop

There's other ways, for example, this question has a very comprehensive comparison between different ways to loop arrays, or even other types of objects.

Last point, because there's some answers using dot notation : since ups is the array with various elements where every element is an object, instead of elem['tt_url'] , you can access their properties using dot, like elem.tt_url , but in this case, that's mostly a matter of preference. In some cases, however, the only option is to use array notation: if you're using a string inside a variable as key, or if the property has some special characters. See this question for more info.