纯 JS 同步 AJAX 调用远程站点

Question

This is what I got:

function fetchJson(url, method, params) {
    var request,
        method = method || 'GET',
        params = params || null;

    if (window.XMLHttpRequest) {
        request = new window.XMLHttpRequest();
    } else {
        try {
            request = new ActiveXObject("MSXML2.XMLHTTP");
        } catch (ex) {
            return null;
        }
    }

    request.open(method, url, false);
    request.send(params);

    if (request.readyState === 4 && request.status === 200)
        return JSON.parse(request.responseText);

    return null;
}

This is supposed to fetch a json synchronously .

However, when I run this in Opera 12 to fetch a Twitter search Json I get an unhandled NETWORK_ERR thrown.

Is it possible to write a pure-JS synchronous ajax function that can fetch json from any location?

Answer 1

Calls using XMLHttpRequest are subject to the Same Origin Policy , which prevents cross-origin calls unless both the server and browser support Cross-Origin Resource Sharing ( most browsers do , although IE8 and IE9's support is broken, requiring use of the MS-specific XDomainRequest object) and the server grants access to the origin of your document.

Absent CORS, there is no direct synchronous solution. You'd have to go indirectly through your own server.

If the twitter feed supports JSONP , though, you can use that, which is asynchronous. Asynchronous requests are generally best in any case.

So summarizing the above, the answer to

Is it possible to write a pure-JS synchronous ajax function that can fetch json from any location?

...is "Yes, if the server supports CORS and allows requests from your origin, and you're using a browser supporting CORS; no if not, you have to go through your own server or do an asynchronous request."

Answer 2

In this case, You have to use jsonp... CrossDomain communication...

I made pure javascript function for you... You can have a look and free to use it

https://github.com/toosha01/ajax-javascript