[英]Cannot read property of array
In my app.js, I have the following: 在我的app.js中,我有以下内容:
post.find({'global': true}).sort('date').exec(function(err, data) {
for (var i = 0; i <= data.length; i++) {
console.log(data[i].email);
//socket.emit('Post', {name: data[i].name, cont: data[i].cont, date: data[i].date});
}
});
When I use 当我使用
console.log(data[i]);
I get my data in the form of 我以以下形式获取数据
{name: blah, cont: blah, email: blah, etc}
But when i try emitting the data 但是当我尝试发射数据时
data[i].attribute
I get the error 我得到错误
TypeError: Cannot read property 'attribute' of undefined
I know the data is there, as I am able to log it in the console. 我知道数据在那里,因为我可以将其记录在控制台中。 Why can't I access the specific attribute of the array? 为什么我不能访问数组的特定属性? Any ideas? 有任何想法吗?
It might be because of how you're using your loop. 可能是因为您如何使用循环。 Your logic with <=
will causes the loop to run one extra time, therefore accessing an array value that doesn't exist. 您使用<=
逻辑将使循环额外运行一次,因此将访问不存在的数组值。 This is a case of what's happening: 这是正在发生的情况:
var data = [{ foo: 'bar1' }, { foo: 'bar2' }];
for (var i = 0; i <= data.length; i++) {
console.log(data[i].foo);
}
The loop will run three times instead of twice, causing this to happen: 该循环将运行3次而不是2次,从而导致这种情况发生:
console.log(data[0].foo); // bar1
console.log(data[1].foo); // bar2
console.log(data[2].foo); // TypeError: Cannot read property 'foo' of undefined
To fix this, change your loop to for (var i = 0; i < data.length; i++)
. 要解决此问题,请将您的循环更改为for (var i = 0; i < data.length; i++)
。
Also, a debugging tip: you should try using output when inspecting errors like yours, even if data
was an array with a length of a thousand, the error would still only be thrown on the last iteration, and with socket.emit()
it would appear as if the loop only ran once. 另外,这是一个调试提示:在检查类似您的错误时,您应该尝试使用输出,即使data
是长度为一千的数组,该错误仍然只会在上一次迭代时抛出,并使用socket.emit()
看起来就像循环只运行一次。
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