遇到JSON和Javascript问题-HavingtroublewithJSONandJavascript

Your code's fine, but $.getJSON just starts the process of getting the JSON file, and then allows your code to continue, calling document.write. The callback to $.getJSON is called later, after your document.write call. Instead, trigger any subsequent code you want to trigger from within the callback.

你的代码很好,但$ .getJSON只是启动获取JSON文件的过程,然后允许你的代码继续,调用document.write。在您的document.write调用之后,稍后将调用$ .getJSON的回调。而是在回调中触发您想要触发的任何后续代码。

You can't usefully use document.write in this situation. You can use the DOM, though, and jQuery's various DOM wrapper functions. For instance:

在这种情况下,您无法有效地使用document.write。但是,您可以使用DOM和jQuery的各种DOM包装函数。例如:

$.getJSON('res/Samples.json',function(data){
    $("
").html(data.length).appendTo(document.body);
});

It's due to the async response from $.getJSON.

这是由于$ .getJSON的异步响应。

var sampleData;
$.getJSON('res/Samples.json', function(data) {
  sampleData = data; // This is occurring after the document.write
});
document.write(sampleData.length);

This is essentially the same as:

这基本上与以下相同:

var sampleData;
setTimeout(function() {
  sampleData = 'Some data'; // This is occurring after the document.write
}, 100);
document.write(sampleData.length);

You could move the document.write to the response handler but as noted below it does have its drawbacks:

您可以将document.write移动到响应处理程序,但如下所述它确实有它的缺点:

var sampleData;
$.getJSON('res/Samples.json', function(data) {
  document.write(sampleData.length); // This would replace the page contents
});

It happens asynchronously, so you need to call document.write in the async call itself:

它是异步发生的,因此您需要在异步调用本身中调用document.write:

var sampleData;
$.getJSON('res/Samples.json',function(data){
    sampleData = data;
    document.write(sampleData.length);
});

Also, if you're using document.write in your production code to write to the page, I would suggest against it. If you used document.write in the above example just for debugging purposes (to figure out why it wasn't working), I would suggest using console.log instead. Much easier.

此外,如果您在生产代码中使用document.write写入页面,我建议不要这样做。如果你在上面的例子中使用document.write只是为了调试目的(弄清楚它为什么不工作),我建议改用console.log。更容易。

$.getJSON is an async function and when you do document.write(sampleData.length);, sampleData is not populated yet.

$ .getJSON是一个异步函数,当你执行document.write(sampleData.length);时,还没有填充sampleData。

You must to do:

你必须这样做:

$.getJSON('res/Samples.json',function(data){
   sampleData=data;
   document.write(sampleData.length);
});

Well is reason is you call the sampleData.length before the ajax call return the values you need to put the document.write(sampleData.length); inside the ajax function

好吧,原因是你在ajax调用之前调用sampleData.length返回你需要放置document.write(sampleData.length);在ajax函数里面