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