Typescript在對象上返回undefined

Question

我有以下代碼。 我從Express Pouchdb拉出對象，然后遍歷_attachments鍵以拉出所有附件。 我有兩個附件：“index”和“toc”。 有趣的部分是“索引”返回它的“數據”屬性罰款，但這一個保持失敗，我不知道為什么。 這就是我將“toc”設置為我的文章對象的方法。

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'];
}

這是控制台的屏幕截圖：

來自PouchDB的相同對象：

{
  "_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"
}

整個項目在這里=> https://github.com/flamusdiu/micro-blog/tree/dev

編輯1

當我從pouchdb中拉出對象時， _attachments會重新映射到attachments 。 更新了代碼以顯示其上方的行。

編輯2從異步調用返回值工作正常。 這一部分沒有錯。 看起來它鏈接到我的第二個電話是修復它的原因。 見下面的答案。

Answer 1

DB查詢是異步調用，循環中的賦值不會在if之前執行。 嘗試這個：

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'];
    }
});