javascript - Why do Firefox and Chrome return different results for tabs.Tab.favIconUrl? And how can I work around this?

Question

The problem

I am writing a WebExtension that makes use of the tab's favicon. I retrieve the URL of the current tab's favicon in this way:

var API = chrome || browser;
API.tabs.query({ active: true, currentWindow: true }, function (tabs) {
    if (tabs[0] && tabs[0].favIconUrl) {
        console.log(tabs[0].favIconUrl);
    }
});

In Firefox, the console logs an image/x-icon data URI representing the image data, but in Chrome, the console logs a plain URL that points to the icon's location. For example, if I run this in stackoverflow.com on Firefox, I get:

data:image/x-icon;base64,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but in Chrome, I get:

https://cdn.sstatic.net/Sites/stackoverflow/Img/favicon.ico?v=ec617d715196

Why this is a problem

I need the data URI because I want to draw the favicon on my own canvas:

var canvas = document.createElement('canvas');
const ctx = canvas.getContext('2d');
const img = new Image();
img.crossOrigin = 'anonymous';
img.src = tabs[0].favIconUrl;
img.decode()
    .then(() => {
        ctx.drawImage(img, 0, 0, size, size);
        // do other stuff on ctx ...
    })
    .catch(err => console.log(err));

This does not work in Chrome because the favicon URL points to a different domain, so I run into this error: Access to image at 'https://cdn.sstatic.net/Sites/stackoverflow/Img/favicon.ico?v=ec617d715196' from origin 'https://stackoverflow.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

and the image decode errors with DOMException: The source image cannot be decoded.

How do I work around this?

Both Mozilla and Google list the same description for Tab.favIconUrl and there is no mention of this difference in behavior here. How else can I retrieve the active tab's favicon Data URI in a cross-browser compatible way?

标签： javascriptgoogle-chromefirefoxgoogle-chrome-extensionfirefox-addon-webextensions

Answer 1

在 Chrome 中，您可以使用网站图标缓存 urlchrome://favicon/https://google.com而不是依赖 Tabs API。有关示例，请参见此：

可靠地在 Chrome 扩展程序中获取 favicon，chrome://favicon?