javascript - How can I detect which browser is used with feature detection? -

i wish detect various browsers feature detection in javascript ie7-11, chrome , firefox. how can this>

as @dandavis said, objects specific browser need. example:

if (!document.characterset || !document.doctype || !document.defaultview) {         /**          * if browser not have these properties on document,          * ie8 or lower... maybe.          */ }