Assign data from jQuery getJSON to array

问题

How do you assign the data fetched via getJSON() to an array, for later use?

The getJSON url below retrieves properly formatted JSON with 10 main elements, each having subelements of id, username, haiku (and other). If you're running it, try saving the JSON elements to a local file, so you won't get the same domain error (i.e., JSON will not load if you're fetching from a different domain).

What happens is that the alert will fetch a value within the getJSON callback, but outside, the value is undefined.


$(document).ready(function(){
    var haikus=[];
    alert("begin loop");
    $.getJSON('http://example.com/json.php',function(data){
         var i=0;
         for(i=0;i<data.length;i++){
            haikus[i]=[data[i].id,String(data[i].username),String(data[i].haiku)];
        }
            alert(haikus[0][1]);
    });
})

Yes, this is related to a previous post. But, I'd initially simplified my problem too much, so the initial solutions provided did not solve it. jQuery - getJSON data to array

回答1:

Your issue is that any code outside (and after) the $.getJSON request has already run by the time the $.getJSON response is received.

Remember that AJAX calls are asynchronous. This means that the code following the AJAX request does not wait for the response to execute. So it runs long before there's any response.

The key is that any code that relies on the response from an asynchronous AJAX request, must run (or be called from) inside the callback.

EDIT:

To clarify, in the code example below, please see the code comments. It should help explain the issue.

$(document).ready(function(){
    var haikus=[];
    alert("begin loop");
    $.getJSON('http://haikuennui.com/random.php',function(data){
         var i=0;
         for(i=0;i<data.length;i++){
            haikus[i]=[data[i].id,String(data[i].username),String(data[i].haiku)];
        }
                 // The data in haikus is available here becuase
                 //    this alert() doesn't run until the response is received.
            alert(haikus[0][1]);
    });

         // Here the data in haikus is NOT available because this line
         //     of code will run ***before*** the response from the AJAX
         //     request from above is received.
         // In other words, this alert() executes **immediately** without
         //     waiting for the $.getJSON() to receive its response.
    alert(haikus[0][1]);

});

回答2:

I believe if you define a variable by using 'var haikus = something', the variable is of local scope, and if you define the variable by using 'haikus = something', it is of global scope.

来源：https://stackoverflow.com/questions/3442487/assign-data-from-jquery-getjson-to-array

标签

jquery

getjson