修改返回

async function handleRequest(request) {
    // 发送原始请求并获取原始结果
    let originalResponse = await fetch(request);
    // 修改body
    let body = JSON.stringify({ foo: 'bar'});
    response = new Response(body, originalResponse);
    // 修改headers
    response.headers.set('foo', 'bar');
    return response;
}
addEventListener('fetch', event => {
    event.respondWith(handleRequest(event.request));
});