Typescript在对象上返回undefined

Question

I have the following code. I pull and object from Express Pouchdb then loop through the _attachments key to pull all the attachments. I have two attachments: "index" and "toc". Fun part is "index" returns it's "data" property fine but this one keeps failing and I have no idea why. This is how I have set the "toc" to my article object.

Object.keys(new_article['attachments']).map((at) => {
    this.articleStore.getAttachment(new_article['id'],at).then ((res) => {
        new_article.attachments[at]['data'] = res.toString();
    });
});

if (new_article['attachments'].hasOwnProperty('toc')) {
    console.log(new_article['attachments']['toc']) //Line #27 in screenshot
    console.log(new_article['attachments']['toc'].data) //Line #28 in screenshot
    new_article.toc = new_article['attachments']['toc']['data'];
}

Here's the screenshot of the console:

The same object from PouchDB:

{
  "_id": "8c0f586b-020b-4832-bcde-945421c22a2e",
  "description": "Getting the Gist of Markdown's Formatting Syntax",
  "author": "John Gruber",
  "title": "Getting the Gist of Markdown's Formatting Syntax",
  "date": "4/15/2017",
  "_attachments": {
    "index.md": {
      "digest": "md5-PjR3R2K+KdpgLy/ye5wgAA==",
      "content_type": "application/octet-stream",
      "length": 8373,
      "revpos": 5,
      "stub": true
    },
    "toc": {
      "digest": "md5-heDcEdGg7nzo0OKe/30YxQ==",
      "content_type": "application/octet-stream",
      "length": 130,
      "revpos": 6,
      "stub": true
    }
  },
  "_rev": "8-167fdf2e930304927c5e2fc4e371b123"
}

The whole project here => https://github.com/flamusdiu/micro-blog/tree/dev

Edit 1

_attachments is remapped to attachments when I pull the object from pouchdb. Updated the code to show the lines above it.

Edit 2 Returning the value from the async call works fine. There is nothing wrong with that part of it. Seems that it's chaining that to my second call is what fixed it. See answer below.

Answer 1

The DB query is an asynchronous call, the assignments in the loop are not executed before the if at the end. Try this:

Promise.all(Object.keys(new_article['attachments']).map((at) => {
    return this.articleStore.getAttachment(new_article['id'],at).then ((res) => {
        new_article.attachments[at]['data'] = res.toString();
    });
})).then(() => {
    if (new_article['attachments'].hasOwnProperty('toc')) {
        console.log(new_article['attachments']['toc']) //Line #27 in screenshot
        console.log(new_article['attachments']['toc'].data) //Line #28 in screenshot
        new_article.toc = new_article['attachments']['toc']['data'];
    }
});