CODE EXAMPLE FOR JAVASCRIPT

react check if string is mail

let handleOnChange = ( email ) => {

    // don't remember from where i copied this code, but this works.
    let re = /^(([^<>()[].,;:s@"]+(.[^<>()[].,;:s@"]+)*)|(".+"))@(([[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}])|(([a-zA-Z-0-9]+.)+[a-zA-Z]{2,}))$/;

    if ( re.test(email) ) {
        // this is a valid email address
        // call setState({email: email}) to update the email
        // or update the data in redux store.
    }
    else {
        // invalid email, maybe show an error to the user.
    }

}