Javascript 使用 dexie db 时以意外顺序调用的函数

Question

我有一个函数在加载页面时执行，该函数调用其他四个函数：

// Initialise DB
await initialiseDb                  ();

// Synchronise server's and local db
await synchroniseClientAndServer    ();

// Use the languages from the local db
addLanguagesToSelection             ();

// Start synchronisation loop
synchroniseClientAndServerLoop      ();

1 - dexie db 的初始化

2 - 从服务器同步数据，将数据保存在本地tables

3 - 使用本地 tables 上保存的数据。

4 - 以 5 秒为间隔执行 #2 的循环

由于某些原因，它们按照#1 #3 #2和#4的顺序执行

async function initialiseDb ()
{
    await database.version ( 1 ).stores ( { values_lookup: '++name, value' } );
    await database.version ( 1 ).stores ( { languages:     '++id, identifier, name'    } );

    languagesTable      = await database.languages;
    valuesLookupTable   = await database.values_lookup;

    // Set synchronisation millisecond = 0 if the database has just been created
    if ( await valuesLookupTable.where ( 'name' ).equals ( "synchronisationMs" ).count () == 0 )
    {
        await valuesLookupTable.put ( { name : 'synchronisationMs', value : 0 } );
    }

    console.log ( "> 111 > valuesLookupTable initialised : " + await valuesLookupTable.where ( 'name' ).equals ( "synchronisationMs" ).count () );
    console.log ( "> 112 > valuesLookupTable initialised : " + await languagesTable.count () );
}


async function synchroniseClientAndServer ()
{
    var previousSyncTime = ( await valuesLookupTable.where ( 'name' ).equals ( "synchronisationMs" ).first () ).value;

    var syncData = JSON.stringify ( { previousSynchronisationTime : previousSyncTime } );

    var xhr = new XMLHttpRequest();
    xhr.open ( "POST", service + "  ClientServerSynchronisation", true );
    xhr.setRequestHeader("Content-Type", "application/json;charset=UTF-8" );
    xhr.send ( syncData );

    xhr.onreadystatechange = async function () 
    {
        // Redirect to home page if sessioin is not active
        if ( this.status === 418 )
        {
            goHome ();
        }
        else if ( this.readyState === 4 && this.status === 200 ) 
        {    
            var syncData = JSON.parse ( xhr.responseText );

            // Update last synchronisation time for the next request
            await database.values_lookup.put ( { name : 'synchronisationMs', value : syncData.synchronisationTime } );

            // Update the list of languages with newly added and deleted
            var updatedLanguages = syncData.updatedLanguages;
            for ( var index = 0; index < updatedLanguages.length; index = index + 1 )
            {
                var language = updatedLanguages [ index ];

                if ( language.addedOrDeleted === ADDED )
                {
                    await languagesTable.put ( { id : language.id, identifier : language.identifier, name : language.name } );
                    console.log ( "> 200 > valuesLookupTable initialised : " + await languagesTable.count () );         
                }
                else
                {
                    await languagesTable.delete ( language.id );
                    console.log ( "> 200 > valuesLookupTable initialised : " + await languagesTable.count () );         
                }
            }
        }
    };
}



async function addLanguagesToSelection ()
{
    console.log ( "> 300 > " );
    var selector = ge ( "languageId" );
    var languages = await languagesTable.toArray ();    
    ....
}

语言table 以上是 table 与语言

结果是这样的：

> 111 > valuesLookupTable initialised : 1 desktop_js.jsp:720:13
> 112 > valuesLookupTable initialised : 0 desktop_js.jsp:721:13

> 300 >                                   desktop_js.jsp:501:10


> 200 > valuesLookupTable initialised : 1 desktop_js.jsp:409:17
> 200 > valuesLookupTable initialised : 2 desktop_js.jsp:409:17
> 200 > valuesLookupTable initialised : 3 desktop_js.jsp:409:17
> 200 > valuesLookupTable initialised : 4 desktop_js.jsp:409:17
> 200 > valuesLookupTable initialised : 5 desktop_js.jsp:409:17
> 200 > valuesLookupTable initialised : 6 desktop_js.jsp:409:17
> 200 > valuesLookupTable initialised : 7 desktop_js.jsp:409:17

所以语言不会出现，因为列表是在加载数据之前填充的。我知道问题可能是 dexie db 是异步的，但我几乎在所有地方都添加了 "await"，它一直是我迄今为止遇到的所有问题的解决方案。

有人能发现我做错了什么吗？

谢谢！

Answer 1

查看您的代码，我最初的想法是您的 synchroniseClientAndServer() 在 addLanguagesToSelection() 之前完成。但是，在synchroniseClientAndServer() 中您有xhr.onreadystatechange，它是异步的并且在程序的其余部分继续运行时等待服务器响应。

本质上顺序是运行这样的：#1,#2,#3,#2.1(xhr.onreadystatechange),#4.

一个解决方案可能是从 xhr.onreadystatechange.

内部调用 addLanguagesToSelection()

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