Javascript 返回未定义的回调
我试图从GMail API获取数据,以便能够从那里加载附件数据base64加密,尽管当我试图返回数据时,我得到的是未定义的数据Javascript 返回未定义的回调,javascript,jquery,asynchronous,callback,gmail-api,Javascript,Jquery,Asynchronous,Callback,Gmail Api,我试图从GMail API获取数据,以便能够从那里加载附件数据base64加密,尽管当我试图返回数据时,我得到的是未定义的数据 $Message['Content']['Attachment'][$Count]['Data'] = getAttachments($Message['Details']['ID'], message['payload']['parts'][key], function (filename, mimeType, attachment) { return 'da
$Message['Content']['Attachment'][$Count]['Data'] = getAttachments($Message['Details']['ID'], message['payload']['parts'][key], function (filename, mimeType, attachment) {
return 'data:'+mimeType+';base64,'+attachment.data.replace(/-/g, '+').replace(/_/g, '/');
});
function getAttachments(messageID, parts, callback) {
var attachId = parts.body.attachmentId;
var request = gapi.client.gmail.users.messages.attachments.get({
'id': attachId,
'messageId': messageID,
'userId': 'me'
});
request.execute(function (attachment) {
callback(parts.filename, parts.mimeType, attachment);
});
}
问题似乎是在函数返回值后数据才可用。这已经通过console.log()进行了测试。它不是返回未定义的回调,而是
getAttachments()
对GMail API的调用是异步的,因此您不能以这种方式分配给$Message…['Data']
——您实际上分配的是getAttachments()
的结果,该结果不返回任何内容,因此未定义
只有在实际回调中,数据才可用,因此需要在回调本身中设置值:
getAttachments($Message['Details']['ID'], message['payload']['parts'][key], function (filename, mimeType, attachment) {
var data = 'data:'+mimeType+';base64,'+attachment.data.replace(/-/g, '+').replace(/_/g, '/');
// now you have the data, you can set the property
$Message['Content']['Attachment'][$Count]['Data'] = data;
});
您可能还需要将$消息的其他处理移动到此处,例如发送。getAttachments()
函数未返回任何值,这就是它未定义的原因
解决方案:
getAttachments($Message['Details']['ID'], message['payload']['parts'][key],function (filename, mimeType, attachment)
{
$Message['Content']['Attachment'][$Count]['Data'] = 'data:'+mimeType+';base64,'+attachment.data.replace(/-/g, '+').replace(/_/g, '/');
});