Calculating size of Google Firestore documents

问题

Firestore docs give details of how to manually calculate the stored size of a document, but there does not seem to be a function provided for this on any of document reference, snapshot, or metadata.

Before I attempt to use my own calculation, does anyone know of an official or unofficial function for this?

Here is my (completely untested) first cut for such a function from my interpretation of the docs at https://firebase.google.com/docs/firestore/storage-size

function calcFirestoreDocSize(collectionName, docId, docObject) {
    let docNameSize = encodedLength(collectionName) + 1 + 16
    let docIdType = typeof(docId)
    if(docIdType === 'string') {
        docNameSize += encodedLength(docId) + 1
    } else {
        docNameSize += 8
    }  
    let docSize = docNameSize + calcObjSize(docObject)

    return  docSize
}
function encodedLength(str) {
    var len = str.length;
    for (let i = str.length - 1; i >= 0; i--) {
        var code = str.charCodeAt(i);
        if (code > 0x7f && code <= 0x7ff) {
            len++;
        } else if (code > 0x7ff && code <= 0xffff) {
            len += 2;
        } if (code >= 0xDC00 && code <= 0xDFFF) {
            i--;
        }
    }
    return len;
}

function calcObjSize(obj) {
    let key;
    let size = 0;
    let type = typeof obj;

    if(!obj) {
        return 1
    } else if(type === 'number') {
        return 8
    } else if(type === 'string') {
        return encodedLength(obj) + 1
    } else if(type === 'boolean') {
        return 1
    } else if (obj instanceof Date) {
        return 8
    } else if(obj instanceof Array) {
        for(let i = 0; i < obj.length; i++) {
            size += calcObjSize(obj[i])
        }
        return size
    } else if(type === 'object') {

        for(key of Object.keys(obj)) {
            size += encodedLength(key) + 1 
            size += calcObjSize(obj[key])
        }
        return size += 32
    }
}

来源：https://stackoverflow.com/questions/49473148/calculating-size-of-google-firestore-documents