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Adaptive Image Resize

Last updated: 2023-07-06 17:20:26
    In this document, we demonstrate how to identify the client type via User-Agent in the request header, use fetch API to get the image from the origin, and convert it to the format required by the browser.
    addEventListener('fetch', event => {
    // If the function code throws an unhandled exception, Edge Functions forwards the current request back to the origin.
    async function handleEvent(event) {
    const { request } = event;
    const urlInfo = new URL(request.url);
    const userAgent = request.headers.get('user-agent');
    // Request a non-image resource
    if (!/\\.(jpe?g|png)$/.test(urlInfo.pathname)) {
    return fetch(request);
    // Image width on the mobile device
    let width = 480;
    const isPcClient = isPc(userAgent);
    // Image width on the PC
    if (isPcClient) {
    width = 1280;
    // Scale the image
    const response = await fetch(request, {
    eo: {
    image: {
    // Set the response header
    response.headers.set('x-ef-client', isPcClient ? 'pc' : 'mobile');
    return response;
    // Identify the request client type
    function isPc(userAgent) {
    const regex = /(phone|pad|pod|iPhone|iPod|ios|iPad|Android|Mobile|BlackBerry|IEMobile|MQQBrowser|JUC|Fennec|wOSBrowser|BrowserNG|WebOS|Symbian|Windows Phone)/i;
    if(regex.test(userAgent)) {
    return false;
    return true;

    Sample Preview

    In the address bar of the browser, enter a URL (such as https://example.com/images-resize/ef-1.jpeg) that matches a trigger rule of the edge function to preview the effect of the sample code.
    For displaying on PC, scale the image to 1280 x 720.
    For displaying on mobile devices, scale the image to 480 x 270.


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