How can you detect if a browser supports NPAPI from JavaScript? Not all of them do, and whilst I could rely on the user-agent I'd much rather do it a more reliable way if one exists.
Unfortunately, I can't simply detect if my plug-in has loaded or not, as it may be that the plugin simply isn't installed yet on a supported browser.
Thanks.
There is no JS API for this, but basically all desktop browsers except IE-/Trident-based ones and ChromeOS support NPAPI.
You can find out wether your plugin is installed by checking navigator.plugins.
If you want to check whether java plugins are enabled or not in the browser then you should use the navigator.javaEnabled(). It will work in chrome.
来源：https://stackoverflow.com/questions/14838739/detecting-npapi-support-using-javascript