How to get something from the state / store inside a redux-saga function?

Question

How do I access the redux state inside a saga function?

Short answer:

import { select } from 'redux-saga/effects';
...
let data = yield select(stateSelectorFunction);

Answer 1

As @markerikson already says, redux-saga exposes a very useful API select() to invoke a selector on the state for getting some part of it available inside the saga.

For your example a simple implementation could be:

/*
 * Selector. The query depends by the state shape
 */
export const getProject = (state) => state.project

// Saga
export function* saveProjectTask() {
  while(true) {
    yield take(SAVE_PROJECT);
    let project = yield select(getProject); // <-- get the project
    yield call(fetch, '/api/project', { body: project, method: 'PUT' });
    yield put({type: SAVE_PROJECT_SUCCESS});
  }
}

In addition to the suggested doc by @markerikson, there is a very good video tutorial by D. Abramov which explains how to use selectors with Redux. Check also this interesting thread on Twitter.