Home >Web Front-end >JS Tutorial >The second day of dojo learning ajax asynchronous request binding list_dojo
Users don’t like scroll bars, so we made tab switching. Users don’t like refreshing the page, so we have to use ajax. In the past few years, almost every web developer was proud to know a little bit of ajax. But knowing that using ajax is not enough, because technology serves people and cannot be abused. You can never make an asynchronous request just to verify a textbox. I also encountered someone who used ajax to update user information. The pictures in the user information were updated using postback. During an update, ajax was stuck there first, and then posted back. How do you think this is? 2 behavior? There are quite a few people like this. I have also encountered someone who uses ajax to update and then locate the location. I don't understand. What's the point of his ajax? It was purely to show that he knew there was such a thing.
Speaking of ajax, I have to talk about the cross-domain problem. When you asynchronously request files under other domain names, access security problems arise. There are many solutions on the Internet, most of which are deceptive. However, there are still two absolutely feasible ways. For example, if you want to asynchronously access cc.ashx under bb.com under aa.com:
1. We can create the dd.ashx file under aa.com, and then use ajax to access the dd.ashx file. At this time, dd.ashx will access cc.ashx under bb.com, because there is no cross-domain problem with background access. , so there is no cross-domain at this time, because what you asynchronously access is still the file dd.ashx in the same domain as aa.com. As for how dd.ashx accesses bb.com, I won’t go into details. You can search for the thief program. The principle is similar.
2. jsonp returns, this method is more popular now, because the first method requires one more request, which will inevitably affect the speed. I don't think the name jsonp is good at all. I prefer to call it "json callback". Its principle is , have you noticed that there is no cross-domain reference to external JS files in this way? What does it have to do with json? jsonp returns a json object on the server side, and performs callbacks on the client to perform related operations on this object. Are you getting less clear the more you listen? I won’t mislead you anymore, just search it yourself.
So, json is very important in the entire js learning (this topic is a bit tough). Generally, ajax returns json, so in dojo, there is another need for json. For some new processing, let’s look at the following code:
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