loginThunk.js

function login(username, password) {
    return dispatch => {
        dispatch({
            type: 'LOGIN_REQUEST'
        })
        api.login(username, password)
            .then(user => dispatch({
                type: 'LOGIN_SUCCESS',
                user
            }))
            .catch(error => dispatch({
                type: 'LOGIN_FAILURE',
                error
            }))
    }
}