如果在Firestore中将日期存储为文档中的timestamp（例如，使用FieldValue.serverTimestamp（）），则以下JavaScript代码将为您提供自storedTimestamp日期以来经过的时间（以毫秒为单位）：

var db = firebase.firestore();

    var docRef = db.collection('yourCollection').doc('yourDocId');

    docRef.get().then(function (doc) {
        if (doc.exists) {
            var storedDate = new Date(doc.data().storedTimestamp);
            var nowDate = new Date();
            var elapsedTime = (nowDate.getTime() - storedDate.getTime());
            console.log(elapsedTime);

        } else {
            // doc.data() will be undefined in this case
            console.log("No such document!");
        }
    }).catch(function (error) {
        console.log("Error getting document:", error);
    });

您还可以使用moment.js库，例如，如下所示，以获取天数差异。

docRef.get().then(function (doc) {
        if (doc.exists) {
            var storedDate = moment(doc.data().storedTimestamp);
            var nowDate = moment();
            //get the difference in days, for example
            console.log(nowDate.diff(storedDate, 'days'))

        } else {
            // doc.data() will be undefined in this case
            console.log("No such document!");
        }
    }).catch(function (error) {
        console.log("Error getting document:", error);
    });