Jquery延迟回调奇怪 [英] Jquery deferred call back oddness
问题描述
jsfiddle.net/austinbv/QVujr/rel =nofollow> http://jsfiddle.net/austinbv/QVujr/
get_each_total = function（callback）{
var requests;
requests = [];
var url;
url =http://otter.topsy.com/search.js?callback=?&apikey=38A260E9D12A4908B1AF9184B691131&q=justin+bieber&window=d;
return requests.push（$。getJSON（url，function（data）{
}））;
return $ .when.apply（$，requests）.then（function（）{
callback（）;
}，function（）{
return alert与远程库通信时出错，请在几个中重试）;
}）;
};
get_each_total_broken = function（callback）{
var requests;
requests = [];
var url;
url =http://otter.topsy.com/hjhkl/sehjkhhkjhkarch.js?callback=?&apikey=38A260E9D12A4908B1AF9184B691131&q=justin+bieber&window=d;
return requests.push（$。getJSON（url，function（data）{
}））;
return $ .when.apply（$，requests）.then（function（）{
callback（）;
}，function（）{
return alert与远程库通信时出错，请在几个中重试）;
}）;
};
$（function（）{
get_each_total（alert（success））;
get_each_total_broken（alert（fail））;
}）;
而这不
http://jsfiddle.net/austinbv/wzve6/
get_each_total = function（callback）{
var requests;
requests = [];
var url;
url =http://otter.topsy.com/search.js?callback=?&apikey=38A260E9D12A4908B1AF9184B691131&q=justin+bieber&window=d;
return requests.push（$。getJSON（url，function（data）{
}））;
return $ .when.apply（$，requests）.then（function（）{
callback（）;
}，function（）{
return alert与远程库通信时出错，请在几个中重试）;
}）;
};
get_each_total_broken = function（callback）{
var requests;
requests = [];
var url;
url =http://otter.topsy.com/hjhkl/sehjkhhkjhkarch.js?callback=?&apikey=38A260E9D12A4908B1AF9184B691131&q=justin+bieber&window=d;
return requests.push（$。getJSON（url，function（data）{
}））;
return $ .when.apply（$，requests）.then（function（）{
callback（）;
}，function（）{
return alert与远程库通信时出错，请在几个中重试）;
}）;
};
$（function（）{
get_each_total（function（）{alert（success）}）;
get_each_total_broken ）;
}）;
，你可以看到唯一的区别是最后两行，其中一个匿名函数包装回调。任何洞察都会很好。
这段代码：
return requests.push（$。getJSON（url，function（data）{
}））;
退出您的函数。 回调从未被调用。
当你说唯一的区别是一个包装回调的匿名函数，这意味着你还在第一个版本的代码中传递一个函数。这不是真的;你试图传入 alert（'whatever'）; 正在返回 undefined
进一步说明：
get_each_total ，& get_each_total_broken ）期望参数是一个函数。这是明显的，你试图调用它作为一个函数后来在你的代码（ callback（））。但是，此行： get_each_total（alert（success））;
不会将函数传递给 get_each_total 。它等价于以下：
var returnedFromAlert = alert（success）;
get_each_total（returnedFromAlert）;
因此，基本上你不会将任何东西传递到 get_each_total 函数。在调用 get_each_total 之前，您会立即收到成功提醒。
I was playing around with call backs and deferred functions in jQuery and was wondering if anyone could tell me why this works
http://jsfiddle.net/austinbv/QVujr/
get_each_total = function(callback) {
var requests;
requests = [];
var url;
url = "http://otter.topsy.com/search.js?callback=?&apikey=38A260E9D12A4908B1AF9184B691131&q=justin+bieber&window=d";
return requests.push($.getJSON(url, function(data) {
}));
return $.when.apply($, requests).then(function() {
callback();
}, function() {
return alert("There was an error communicating with a remote library, try again in a few");
});
};
get_each_total_broken = function(callback) {
var requests;
requests = [];
var url;
url = "http://otter.topsy.com/hjhkl/sehjkhhkjhkarch.js?callback=?&apikey=38A260E9D12A4908B1AF9184B691131&q=justin+bieber&window=d";
return requests.push($.getJSON(url, function(data) {
}));
return $.when.apply($, requests).then(function() {
callback();
}, function() {
return alert("There was an error communicating with a remote library, try again in a few");
});
};
$(function () {
get_each_total(alert("success"));
get_each_total_broken(alert("fail"));
});
and this does not
http://jsfiddle.net/austinbv/wzve6/
get_each_total = function(callback) {
var requests;
requests = [];
var url;
url = "http://otter.topsy.com/search.js?callback=?&apikey=38A260E9D12A4908B1AF9184B691131&q=justin+bieber&window=d";
return requests.push($.getJSON(url, function(data) {
}));
return $.when.apply($, requests).then(function() {
callback();
}, function() {
return alert("There was an error communicating with a remote library, try again in a few");
});
};
get_each_total_broken = function(callback) {
var requests;
requests = [];
var url;
url = "http://otter.topsy.com/hjhkl/sehjkhhkjhkarch.js?callback=?&apikey=38A260E9D12A4908B1AF9184B691131&q=justin+bieber&window=d";
return requests.push($.getJSON(url, function(data) {
}));
return $.when.apply($, requests).then(function() {
callback();
}, function() {
return alert("There was an error communicating with a remote library, try again in a few");
});
};
$(function () {
get_each_total(function () { alert("success")});
get_each_total_broken(function () {alert("fail")});
});
as you can see the only difference is in the last two lines, where an anonymous function wraps the callback. Any insight would be nice.
This piece of code:
return requests.push($.getJSON(url, function(data) {
}));
exits out of your function. The callback is never called.
P.S. When you're saying the only difference is an anonymous function wrapping the callback, you imply that you're also passing a function in the first version of your code. That is not true; you're trying to pass in whatever alert('whatever'); is returning, which is undefined!
Further explanation:
Both of your functions (get_each_total, & get_each_total_broken) expect the parameter to be a function. This is evident by you trying to call it as a function later on in your code (callback()). However, this line:
get_each_total(alert("success"));
does not pass a function to get_each_total. It is equivalent to the following:
var returnedFromAlert = alert("success");
get_each_total(returnedFromAlert);
So, basically, you're not passing anything into your get_each_total function. You get a success alert right away, before get_each_total has been called.
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