javascript - undefined object

Question

我正在传递一个对象 "text":"Hey! my chat text here"进入 DOM 中的 div 标签 我正在使用 pubnub 流 API。我的问题是 undefined为每个没有 "text":"Hey! my chat text here" 的对象显示当连接到 channel 时，这发生在 <div id="textbox"></div> 内部.我如何摆脱 undefined ？

undefined
undefined
undefined
Hey, my chat text
undefined
undefined
undefined
undefined

javascript代码

<script src="http://cdn.pubnub.com/pubnub-3.7.15.min.js"></script>
<script charset="utf-8">
    PUBNUB.bind('load', window, function frontpageDemo() {

        var PUBNUB_demo = PUBNUB.init({
            subscribe_key: 'subkey_here',
        });

        PUBNUB_demo.subscribe({
            'channel': "my_channel_here",
            'connect': function(c) {
                console.log('CONNECTED to ' + c);
            },
            'callback': function(m, a, subscribed_channel, c, real_channel) {
                console.log(JSON.stringify(m));
                console.log(JSON.stringify(subscribed_channel));
                console.log(JSON.stringify(real_channel));
                document.getElementById('textbox').innerHTML = '<div>' + m.text + '</div>' + document.getElementById('textbox').innerHTML;
            }
        })

    });
</script>

Answer 1

好的，我解决了这个问题，显然我需要一个 if 和 else 语句

PUBNUB_demo.subscribe({
            'channel': "my_channel_here",
            'connect': function(c) {
                console.log('CONNECTED to ' + c);
            },
            'callback': function(m, a, subscribed_channel, c, real_channel) {
                console.log(JSON.stringify(m));
                console.log(JSON.stringify(subscribed_channel));
                console.log(JSON.stringify(real_channel));
                if (m.text === undefined) {}
                else {document.getElementById('textbox').innerHTML = '<div>' + m.text + '</div>' + document.getElementById('textbox').innerHTML;
}
        })

关于 undefined objects 的更多信息在 MDN