Typescript TypeError: Cannot read property 'collection' of undefined

Question

I'm getting an error of 'collection' undefined when trying to push object.

groupShortlists(lists: ProductShortlist[]) {
    const grouped = lists.reduce((groupedList, list) => {
        groupedList[list.collection] = [...groupedList[list.collection] || [], list];
        return groupedList;
      }, {});

    return Object.keys(grouped).map(key => grouped[key]);
  }


this.shortlistsCategory = [];
this.groupShortlists(this.shortLists).map((item, key) => {
      this.shortlistsCategory.push({
        collection: item[key].collection,
        list: [],
      });
    });

The exact error says:

TypeError: Cannot read property 'collection' of undefined

Is this the proper way of using push. Any help would be appreciated. :D

In map function, the first arg will be a single obj/item of that array and the second will be index. So make sure item[0] exists. — Yashwardhan Pauranik
– Yashwardhan Pauranik, Commented Nov 13, 2019 at 3:01
What does groupShortlists do? Can you include a code snippet please — christian
– christian, Commented Nov 13, 2019 at 3:50
After seeing your snippet for the groupShortlist method, it looks like the returned array may have nested arrays (which could be an issue). Can you post an example of ProductShortlist? — christian
– christian, Commented Nov 13, 2019 at 12:14

christian · Accepted Answer · 2019-11-13 04:02:18Z

1

In this scenario, the item is already the value at the index key of shortLists. You can do either item.collection or shortLists[key].collection, but not both.

Also, using .map already returns the specified object, so there's no need to use .map and a .push (it's not as semantic).

Below is an example setting shortlists category to the .map return value.

this.shortlistsCategory = this.groupShortlists(this.shortLists)
  .map(item => {
    return {
      collection: item.collection,
      list: []
    };
  });

Link to .map docs: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map

answered Nov 13, 2019 at 4:02

christian

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