javascript - jsonp can only use get reason

Question

Why can jsonp only use get requests? Is it because of some reasons of get, some reasons of post, or some other reasons? I checked the document and it said that 'this is determined by the characteristics of the technology itself'. Can you tell me about this? What does the characteristic mean? Can you explain it in detail? Many thanks!

PHP中文网 · Answer

JSONP is a
【request a JS script and use the result of executing this script as data】
method.

So, can you POST a script introduced through the script tag?

(If you have read the source code of the JSONP library, you will know that the common implementation code is actually document.createElement('script') to generate a script tag and then insert it into the body. There is no room to set the request format here).

世界只因有你 · Answer

The JS code in domain name A AJAX requests server data with domain name B. This is a cross-domain AJAX request, which is not possible by default.

But there are places in HTML where cross-domain requests can be made, such as img script tags. Their src attributes point to addresses that are not under domain name A (that is, cross-domain).

Then someone took advantage of the above characteristics, chose the feature of src in script that can obtain content across domains, and developed a hack protocol like JSONP. (Requests in src are all GET)

That assumes the JSONP request is as follows:

jsonp({
    url: 'http://path/to/server/b',
    params: {A: a, B: b},
    success: function myCallback (response) {}
})

What’s going on behind the scenes:

Splice a script tag, , thereby triggering a GET to the specified address Request
The server processes this GET request and returns the string "myCallback('response value')"
After the front-end script is loaded, it is actually executed in the scriptmyCallback('response value')
Have the cross-domain request been completed?
Is it just possible to use GET

黄舟 · Answer

Similar to dynamically adding a js code to your page, do you think the js file can be posted?

给我你的怀抱 · Answer

Suppose the address you requested returns a web page like this.




    
    Document

The browser needs to parse this webpage after getting it, and parse it to

When I read this line of code, I knew that a js file was needed here, so I initiated another request to get this js file. This request can only use the GET method, not POST, just like you enter the address in the browser address bar. It’s the same as pressing Enter to enter.

The implementation principle of JSONP is to create a script tag, and then put the api address that needs to be requested in src. So it can only be GET.

代言 · Answer

Because of the

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