Questions about Access Control allow Origin error

The first time the day before yesterday a GET request was sent to the server using jquery. The result was a sucking-up. Check the console tip saying "No ' Access-control-allow-origin ' header is present on the requested resource. Origin ' null ' is therefore not allowed access. "Yes, well, Google didn't know it was a cross-domain issue.

Cross-domain access: AJAX cross-domain access is the cross-domain access request to the B site that is generated when a user accesses a site, which is submitted to the specified page of site A-Baidu encyclopedia

and search some articles, my understanding is that JavaScript has the same origin policy restrictions, JS file can only operate to obtain the same domain name, the same port data. So when I open the HTML locally and make a request to the server, it is rejected at first-it's no problem to put the HTML file you wrote on the server and open it.

(This is not very troublesome, every time you modify the point of everything must be submitted to the test??? ）

Fortunately, jquery encapsulates the functionality of the JSONP.

About Jsonp (JSON with Padding)

Note that JSON and JSONP differ greatly! JSON is a lightweight data format, and JSONP can be understood as a protocol. The above mentioned JavaScript has a homologous strategy, but it does not make physical damage to some tags (script, iframe, IMG, etc. with SRC attribute tags). The core of JSONP is to use the script tag to invoke the JS script provided by the server, while JSON is native to JavaScript, so the JSONP is to treat the resulting JSON data as javascrip objects, so there is no cross-domain problem.

Jsonp How to use JavaScript Demo

    //function called after the server returns results    var Callback = function(Data){        Console.Log(Data);    };    //provide the URL address of the JSONP service (regardless of the type of address, the resulting return value is a piece of JavaScript code)    var URL = "Http://yoururl.com";    //Create a script tag, set its properties    var Script = Document.createelement(' script ');    Script.SetAttribute(' src ', URL);    //Add the script tag to head, at which point the call begins    Document.getElementsByTagName(' head ')[0].appendchild(Script); 

jquery Demo

$.Ajax({        type: "Get",        URL:"Http://yoururl.com",        DataType: "Jsonp",        Data: {        },        //When the server returns and calls the Success function directly, it is not necessary for us to define the callback.         Success: function(Object) {            Console.Log(Object);        }})

Recommended reading:

• Talking about cross-domain

• Talk about JSON and JSONP, maybe you'll be enlightened, with jquery use cases

• Baidu Encyclopedia--jsonp

Questions about Access Control allow Origin error