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This is a glossary of the core terms in Redux Saga.


An effect is a plain JavaScript Object containing some instructions to be executed by the saga middleware.

You create effects using factory functions provided by the redux-saga library. For example you use call(myfunc, 'arg1', 'arg2') to instruct the middleware to invoke myfunc('arg1', 'arg2') and return the result back to the Generator that yielded the effect


A task is like a process running in background. In a redux-saga based application there can be multiple tasks running in parallel. You create tasks by using the fork function

import {fork} from "redux-saga/effects"

function* saga() {
const task = yield fork(otherSaga, ...args)

Blocking/Non-blocking call

A Blocking call means that the Saga yielded an Effect and will wait for the outcome of its execution before resuming to the next instruction inside the yielding Generator.

A Non-blocking call means that the Saga will resume immediately after yielding the Effect.

For example

import {call, cancel, join, take, put} from "redux-saga/effects"

function* saga() {
yield take(ACTION) // Blocking: will wait for the action
yield call(ApiFn, ...args) // Blocking: will wait for ApiFn (If ApiFn returns a Promise)
yield call(otherSaga, ...args) // Blocking: will wait for otherSaga to terminate

yield put(...) // Non-Blocking: will dispatch within internal scheduler

const task = yield fork(otherSaga, ...args) // Non-blocking: will not wait for otherSaga
yield cancel(task) // Non-blocking: will resume immediately
// or
yield join(task) // Blocking: will wait for the task to terminate


refers to a way of organizing the control flow using two separate Sagas

  • The watcher: will watch for dispatched actions and fork a worker on every action

  • The worker: will handle the action and terminate


function* watcher() {
while (true) {
const action = yield take(ACTION)
yield fork(worker, action.payload)

function* worker(payload) {
// ... do some stuff