试图提取 LRS 记录的某些数据片段，需要 catch-try 帮助

Question

我有一个已完成 90% 并且可以正常工作的脚本。我正在使用旧代码获取 LRS 语句。就是使用tincan.js的那个。我正在尝试下拉并解析以下内容：Actor、动词、对象、时间戳和 id under contextActivities。这是最后一个让我感到不适的人。你能看看我最后的 catch/try 陈述并告诉我哪里错了吗？谢谢。

<!DOCTYPE  html>
<!--Parsing "resumed" statements-->
<html lang='en'> 
    <head> 
        <meta charset='UTF-8'> 
        <title>Get my Statements</title> 
        <script type="text/javascript" src="build/tincan.js"></script> 
    </head> 
    <body> 
        <h1>Get statements  101</h1> 
        <div id='response'></div>
        <script>
      var lrs;

try {
    lrs = new TinCan.LRS(
        {

            endpoint: "https://lrs.adlnet.gov/xapi/",
            username: "xapi-tools",
            password: "xapi-tools",
            allowFail: false
        }
    );
}
catch (ex) {
    console.log("Failed to setup LRS object: " + ex);
    // TODO: do something with error, can't communicate with LRS
}


//Pulls all of the resumed statements

lrs.queryStatements(
    {
        params: {
            verb: new TinCan.Verb(
                {
                    id: "http://adlnet.gov/expapi/verbs/completed"
                }
            ),
            since: "2016-01-05T08:34:16Z"
        },
        callback: function (err, sr) {
            if (err !== null) {
                console.log("Failed to query statements: " + err);
                // TODO: do something with error, didn't get statements
                return;
            }

            if (sr.more !== null) {
                // TODO: additional page(s) of statements should be fetched
            }

            var container =  document.getElementById('response');
            //container.innerHTML = (err !== null ? 'ERROR' : JSON.stringify(sr.statements));
            container.innerHTML = (err !== null ? 'ERROR' : parseMyData(sr));
        }
    }
);


parseMyData = function(result) {
            var statements = result.statements;
            var output = '';
            var name,verb,activity, timestamp, context;
            for(var i=0;i<statements.length;i++){
                // check the statement for a usable name value
                // (priority = actor.name, actor.mbox, actor.account.name)
                if(statements[i].actor.name != null && statements[i].actor.name != "") {
                    name = statements[i].actor.name
                }else if(statements[i].actor.mbox != null && statements[i].actor.mbox != "") {
                    name = statements[i].actor.mbox
                }else{
                    name = statements[i].actor.account.name
                }
                // check the statement for a usable verb value
                // (priority = verb.display['en-US'], verb.id)
                try{
                    verb = statements[i].verb.display['en-US'];
                }catch(e){
                    verb = statements[i].verb.id;
                }
                // check the activity for a usable value
                // (priority = definition.name['en-US'], id)
                try{
                    activity = statements[i].target.definition.name['en-US'];
                }catch(e){
                    activity = statements[i].target.id;
                }
                try{
                    timestamp = statements[i].timestamp;
                }catch(e){
                    timestamp = statements[i].timestamp;
                }

                try{
                    context = statements[i].target.contextActivities.other['id'];
                }catch(e){
                    context = statements[i].activity.other['id'];
                }

                output +=   name + ' - ' +
                            verb + ' - ' + 
                            activity + ' - ' +
                            timestamp + ' - ' +
                            context +
                            '<br>' 
            }
            return output;
}

        </script> 
    </body> 
</html>

Answer 1

您正在尝试访问永远不会存在的属性：

statements[i].target.contextActivities

当它存在时，它的最后一部分将存在于 statements[i].context 中，除非您提前知道声明，否则并不总是如此。在访问它们之前，几乎所有的属性都应该检查 null，这样做将允许您删除 try/catch 块。属性名称本身非常稳定，库明确地将 null 值分配给已知属性。此外，other 属性将包含一组活动（当它被填充时），因此您应该通过索引访问它们，因此 contextActivities.other[0].id 等

对于 target 属性您应该检查它是否是特定 class 的实例，因为它可以包含多种类型的对象（actor 但他们有效匹配）。一般来说，对于此特定任务，您可能还希望尽可能利用 toString 方法，它们的工作非常相似。

试图提取 LRS 记录的某些数据片段，需要 catch-try 帮助

Trying to pull certain data pieces of an LRS record, need catch-try assistance

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