如何将数据从Firestore转换为全局变量? [英] How to make the data from Firestore in to a global variable?

问题描述

如何使值返回到onSnapshot函数之外?

How can I make the value return outside the onSnapshot function?

function checkIfExisting(){

  const collection = firebase.firestore().collection("audit");
  const getCaseID = collection.where("caseID", "==", "00001234");

  getCaseID.onSnapshot(function(querySnapshot) {
    let wordLists = [];
    querySnapshot.forEach(function(doc) {
    //get all the scanned words under "word" field in the Firestore Database
        wordLists.push(doc.data().word);
    });

    console.log("words: ", wordLists);// return a value

  });

  console.log("words1: ", wordLists);// undefined

  }

我知道 console.log("words1:"，wordLists)在函数之外，这就是为什么我无法获得其值的原因.您能否给我一个关于如何在函数外部调用它的想法(如果可能的话).

I knew that the console.log("words1: ", wordLists) is outside the function that's why I can't get its value. Could you please give me an idea on how can I call it outside the function (if possible).

推荐答案

要在外部访问它，可以使用 Promise :

To access it outside, you can use Promise:

function checkIfExisting(){
  return new Promise((resolve, reject) => {
   const collection = firebase.firestore().collection("audit");
   const getCaseID = collection.where("caseID", "==", "00001234");

   getCaseID.get().then(function(querySnapshot) {
     let wordLists = [];
     querySnapshot.forEach(function(doc) {
     //get all the scanned words under "word" field in the Firestore Database
        wordLists.push(doc.data().word);
          resolve(wordLists);
     });
     console.log("words: ", wordLists);// return a value
  });

然后访问外部，请执行以下操作:

Then to access outside do the following:

checkIfExisting().then((result) => {
   console.log(result);
});

结果将包含 wordLists

检查以下内容以获取更多信息:

Check the following for more information:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise

这篇关于如何将数据从Firestore转换为全局变量?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！