javascript - How to determine if a Promise is supported by the browser

Question

Does anyone know, using Modernizr or otherwise, if there is a way to detect if the Promise feature is enabled in a browser?

I have a polyfill for the functionality, but only want to apply it if the browser does not have a native implementation.

Answer 1

Update Dec 11 - 2016: All evergreen versions of browsers now support promises. They are safe to use.

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Update Nov 14 - 2016: Chrome, Firefox, Safari and IE all now have experimental support for promises in their dev channels. The specification has settled. I would still not rely on the implementation just yet and would use a library but this might change in a few months.

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No browsers support promises natively in a reliable way. The specification might change - at least for a few more months. My suggestion is use a fast promise library like Bluebird.

If you want to check if native promises are enabled - you can do :

if(typeof Promise !== "undefined" && Promise.toString().indexOf("[native code]") !== -1){
    //here
}

As others suggested, just checking if there is a Promise object can be done by if(Promise) but I strongly suggest against it since different libraries have different APIs for creation of promises etc.