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.

what is your variable 'ups' that you are using in for statement? — Paulo Barbosa, Jul 15 '22 at 14:29
Your latest error means that the object has no `tt_url` property. Make sure to debug and inspect your variables as you run the code with break points. It is so much easier when you spot that a variable has not the expected value. — trincot, Jul 15 '22 at 14:30
change var ups_tt = i['tt_url'] with var ups_tt = ups[i]['tt_url'] . i is just an integer — R4ncid, Jul 15 '22 at 14:33

score 0 · Answer 1 · answered Jul 15 '22 at 14:35

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];

score 0 · Answer 2 · edited Jul 17 '22 at 08:41

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)
});

console.log(element.article_code) you can access the value like this — Rajesh, Jul 15 '22 at 14:37
Your answer could be improved by adding more information on what the code does and how it helps the OP. — Tyler2P, Jul 17 '22 at 08:41

score 0 · Accepted Answer · answered Jul 15 '22 at 14:40

0

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;

answered Jul 15 '22 at 14:40

Mr. Innovator

95
1
6

ended up doing this too, thank you for suggesting – X13Theo Jul 22 '22 at 14:09

user19513069 · Answer 4 · 2022-07-15T15:14:17.547

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 (e.g., 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.

Iterate through an array of objects Nodejs

4 Answers4