Cloudflare已经成为许多网站优选的服务提供商，它的免费CDN(Content Delivery Network)服务以及高效的Workers功能，不仅加快了网站的访问速度，也提供了丰富的操作可能。

在这里，我会具体介绍如何利用Cloudflare Workers来实现反向代理，从而加速国外网站的访问，更进一步的，你或许可以实现在不翻墙的情况下访问某些网站，这无疑给我们带来了更多便利。

在开始之前，我们先了解一下Cloudflare Workers的基础知识。它是一种能在全球范围内运行 JavaScript、Rust 和 C 等编程语言的高性能边缘计算服务。也就是说，你能够在离用户最近的地方执行代码，无需考虑服务器或操作系统，这是为何称其作无服务器（Serverless）技术的原因。可以简单的认为，Cloudflare Workers确实就像是一种可以让你的代码在云端运行的虚拟服务器。

一个更直观的理解是，你可以把Cloudflare Workers想象成是运行在云端的个人计算机，你可以在上面部署JavaScript脚本进行各种操作。当有人尝试访问你的网站时，Cloudflare Workers会在接收到请求后，在边缘节点执行你部署的脚本并返回结果，从而极大的加速了响应速度。

所以，借助Cloudflare Workers，我们可以实现从浏览器到服务器的最短路径，为用户创建无缝、快速的网络体验。

最简单的方法如下：

addEventListener(
   "fetch",event => {
        let url=new URL(event.request.url);
        url.hostname="反代域名（不需要https://）";
        let request=new Request(url,event.request);
        event. respondWith(
                fetch(request)
        )
    }
)

自定义一些参数，相对比较复杂：

// Website you intended to retrieve for users.
const upstream = 'example.com'

// Custom pathname for the upstream website.
const upstream_path = '/'

// Website you intended to retrieve for users using mobile devices.
const upstream_mobile = 'example.com'

// Countries and regions where you wish to suspend your service.
const blocked_region = ['KP', 'HK']

// IP addresses which you wish to block from using your service.
const blocked_ip_address = ['0.0.0.0', '192.168.1.1']

// Whether to use HTTPS protocol for upstream address.
const https = true

// Whether to disable cache.
const disable_cache = false

// Replace texts.
const replace_dict = {
    '$upstream': '$custom_domain'
}

addEventListener('fetch', event => {
    event.respondWith(fetchAndApply(event.request));
})

async function fetchAndApply(request) {

    const region = request.headers.get('cf-ipcountry').toUpperCase();
    const ip_address = request.headers.get('cf-connecting-ip');
    const user_agent = request.headers.get('user-agent');

    let response = null;
    let url = new URL(request.url);
    let url_hostname = url.hostname;

    if (https == true) {
        url.protocol = 'https:';
    } else {
        url.protocol = 'http:';
    }

    if (await device_status(user_agent)) {
        var upstream_domain = upstream;
    } else {
        var upstream_domain = upstream_mobile;
    }

    url.host = upstream_domain;
    if (url.pathname == '/') {
        url.pathname = upstream_path;
    } else {
        url.pathname = upstream_path + url.pathname;
    }

    if (blocked_region.includes(region)) {
        response = new Response('Access denied: WorkersProxy is not available in your region yet.', {
            status: 403
        });
    } else if (blocked_ip_address.includes(ip_address)) {
        response = new Response('Access denied: Your IP address is blocked by WorkersProxy.', {
            status: 403
        });
    } else {
        let method = request.method;
        let request_headers = request.headers;
        let new_request_headers = new Headers(request_headers);

        new_request_headers.set('Host', upstream_domain);
        new_request_headers.set('Referer', url.protocol + '//' + url_hostname);

        let original_response = await fetch(url.href, {
            method: method,
            headers: new_request_headers
        })

            let original_response_clone = original_response.clone();
        let original_text = null;
        let response_headers = original_response.headers;
        let new_response_headers = new Headers(response_headers);
        let status = original_response.status;

        if (disable_cache) {
            new_response_headers.set('Cache-Control', 'no-store');
        }

        new_response_headers.set('access-control-allow-origin', '*');
        new_response_headers.set('access-control-allow-credentials', true);
        new_response_headers.delete('content-security-policy');
        new_response_headers.delete('content-security-policy-report-only');
        new_response_headers.delete('clear-site-data');

        if (new_response_headers.get("x-pjax-url")) {
            new_response_headers.set("x-pjax-url", response_headers.get("x-pjax-url").replace("//" + upstream_domain, "//" + url_hostname));
        }

        const content_type = new_response_headers.get('content-type');
        if (content_type != null && content_type.includes('text/html') && content_type.includes('UTF-8')) {
            original_text = await replace_response_text(original_response_clone, upstream_domain, url_hostname);
        } else {
            original_text = original_response_clone.body
        }

        response = new Response(original_text, {
            status,
            headers: new_response_headers
        })
    }
    return response;
}

async function replace_response_text(response, upstream_domain, host_name) {
    let text = await response.text()

        var i,
    j;
    for (i in replace_dict) {
        j = replace_dict[i]
            if (i == '$upstream') {
                i = upstream_domain
            } else if (i == '$custom_domain') {
                i = host_name
            }

            if (j == '$upstream') {
                j = upstream_domain
            } else if (j == '$custom_domain') {
                j = host_name
            }

            let re = new RegExp(i, 'g')
            text = text.replace(re, j);
    }
    return text;
}

async function device_status(user_agent_info) {
    var agents = ["Android", "iPhone", "SymbianOS", "Windows Phone", "iPad", "iPod"];
    var flag = true;
    for (var v = 0; v < agents.length; v++) {
        if (user_agent_info.indexOf(agents[v]) > 0) {
            flag = false;
            break;
        }
    }
    return flag;
}