javascript - react isomirphic-fetch promise chaining -

okay, understood promise chain works keep returning promise inside previous promise response function:

somepromise.then(function(response){   return anotherpromise(response.data); <- promise returning function }).then(function(response){   return yetanotherpromise(response.data); <- promise returning function }).then(function(response){    itisdone(response.data); }).catch(function(err){   someerrorhandling(err); }); 

if of promise returning function remove chain no continue. , yet today proved me wrong when did in react isomorphic-fetch.

inside auth service;

login: function (email, password) {      let promise = fetch('http://localhost:3000/auth/login', {         method : 'post',         body   : json.stringify({email, password}),         headers: {             'content-type': 'application/json'         }     });      promise.then(function (res) {         if (validator.isjson(res))             return res.json();     }).then(function (parseddata) {         if (parseddata.access_token !== undefined)             localstorage.setitem('access_token', parseddata);     }).then(function () {         console.log('it crazy');     });      return promise; }, 

inside app:

login(){     auth.login(this.state.email, this.state.password).then(() => {         notificationmanager.success('successful login');     }).catch((err) => {         notificationmanager.error(err.message);     }); } 

in case of error (if response not json) token should not saved because res.json() function not returned, causing chain stop. yet line "it crazy" printed out, why?