jquery - Pure HTML form works, same query with Ajax fails -

this html forms send request, , google authentication works :

<form action="/auth/google" method="get">     <button type="submit">         login google     </button> </form> 

however, content of response (json) displayed in browser, html page, , replaces current page, reason. if prevent form submitting (i.e. e.preventdefault()), nothing happens @ all. don't know how catch json.

so i'm trying make same call using ajax

<button type="submit" id="btngoogle">     login google </button>  <script>      $('#btngoogle').click( (e) => {          $.ajax({                 type: "get",                 url :"/auth/google",                 datatype : "json",                 crossdomain : true, // no effect                 headers : {                     // tried many headers, no effect                 }             })             .success( (data) => {                 console.log("success!", data))             })             .error( (err) => {                 console.error(err.statustext);             })         });      </script> 

but cross-domain error

xmlhttprequest cannot load https://accounts.google.com/o/oauth2/v2/auth?response_type=code&redirect_ur…d=178168129307-5g50gah2he0gjjl2or73a1va8ha66s24.apps.googleusercontent.com. no 'access-control-allow-origin' header present on requested resource. origin 'http://localhost:8100' therefore not allowed access.

on node/express server :

app.get('/auth/google',     passport.authenticate('google', {         scope: ['https://www.googleapis.com/auth/plus.profile.emails.read']     })); 

how come html form, reaches same server route same parameters, makes it,but ajax call doesn't?

edit

i have found workaround installing cors extension chrome, so... yeah, kind of works, why ajax call need this, whereas regular html form doesn't?

re: why ajax call need this, whereas regular html form doesn't":

your basic ajax calls cannot process server redirects @ all, cannot handle redirect google's oauth system.

to avoid problem oauth providers had ensure login links not handled ajax , allowed browser handle redirects.

using iframe handle external login , subsequent redirects option if want appear spa.