react native - this.props.navigation loses value when called in my POST method -


inside register page have method gets called , register's user. when try navigate login page after registering user cannot read property 'navigation' of undefined. code 

sendajax = () => {   //this.props.navigation returns value , can navigate 'login'    if(!regex.test(this.state.email)){   }else if(this.state.password != this.state.confirmpwd){     alert.alert("the passwords don't match!");   }else{     const fn = encodeuricomponent(this.state.firstname);     ...     const hashdigest = sha256(p);     const requestbody = `firstname=${fn}...      //post     fetch("http://localhost:3000/users", {         method: "post",         mode: "cors",         headers: {             "content-type": "application/x-www-form-urlencoded"         },         body: requestbody     }).then(function (res, next) {         console.log("fetch request ", json.stringify(res.ok));         if(res.ok){             res.json().then(function (json) {                 if(json.registerstate){                     alert.alert('register success, please login');                     //cannot read property 'navigation' of undefined                     this.props.navigation.navigate('login')                 }             });         }     })     .then((res) => {       alert.alert("then working");     })     ....   } }

i'm not sure why this.props.navigation.navigate becomes undefined halfway down method, yet @ beginning call it. great, thanks!

this issue "this" changing you. using arrow functions keeps "outer this" in scope, instead of "this" changing because of being in new function.


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