redux-saga/es/internal/channel.js

Saga middleware for Redux to handle Side Effects

var _extends = Object.assign || function (target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i]; for (var key in source) { if (Object.prototype.hasOwnProperty.call(source, key)) { target[key] = source[key]; } } } return target; };

import { is, check, remove, MATCH, internalErr, SAGA_ACTION } from './utils';
import { buffers } from './buffers';
import { asap } from './scheduler';

var CHANNEL_END_TYPE = '@@redux-saga/CHANNEL_END';
export var END = { type: CHANNEL_END_TYPE };
export var isEnd = function isEnd(a) {
  return a && a.type === CHANNEL_END_TYPE;
};

export function emitter() {
  var subscribers = [];

  function subscribe(sub) {
    subscribers.push(sub);
    return function () {
      return remove(subscribers, sub);
    };
  }

  function emit(item) {
    var arr = subscribers.slice();
    for (var i = 0, len = arr.length; i < len; i++) {
      arr[i](item);
    }
  }

  return {
    subscribe: subscribe,
    emit: emit
  };
}

export var INVALID_BUFFER = 'invalid buffer passed to channel factory function';
export var UNDEFINED_INPUT_ERROR = 'Saga was provided with an undefined action';

if (process.env.NODE_ENV !== 'production') {
  UNDEFINED_INPUT_ERROR += '\nHints:\n    - check that your Action Creator returns a non-undefined value\n    - if the Saga was started using runSaga, check that your subscribe source provides the action to its listeners\n  ';
}

export function channel() {
  var buffer = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : buffers.fixed();

  var closed = false;
  var takers = [];

  check(buffer, is.buffer, INVALID_BUFFER);

  function checkForbiddenStates() {
    if (closed && takers.length) {
      throw internalErr('Cannot have a closed channel with pending takers');
    }
    if (takers.length && !buffer.isEmpty()) {
      throw internalErr('Cannot have pending takers with non empty buffer');
    }
  }

  function put(input) {
    checkForbiddenStates();
    check(input, is.notUndef, UNDEFINED_INPUT_ERROR);
    if (closed) {
      return;
    }
    if (!takers.length) {
      return buffer.put(input);
    }
    for (var i = 0; i < takers.length; i++) {
      var cb = takers[i];
      if (!cb[MATCH] || cb[MATCH](input)) {
        takers.splice(i, 1);
        return cb(input);
      }
    }
  }

  function take(cb) {
    checkForbiddenStates();
    check(cb, is.func, "channel.take's callback must be a function");

    if (closed && buffer.isEmpty()) {
      cb(END);
    } else if (!buffer.isEmpty()) {
      cb(buffer.take());
    } else {
      takers.push(cb);
      cb.cancel = function () {
        return remove(takers, cb);
      };
    }
  }

  function flush(cb) {
    checkForbiddenStates(); // TODO: check if some new state should be forbidden now
    check(cb, is.func, "channel.flush' callback must be a function");
    if (closed && buffer.isEmpty()) {
      cb(END);
      return;
    }
    cb(buffer.flush());
  }

  function close() {
    checkForbiddenStates();
    if (!closed) {
      closed = true;
      if (takers.length) {
        var arr = takers;
        takers = [];
        for (var i = 0, len = arr.length; i < len; i++) {
          arr[i](END);
        }
      }
    }
  }

  return {
    take: take,
    put: put,
    flush: flush,
    close: close,
    get __takers__() {
      return takers;
    },
    get __closed__() {
      return closed;
    }
  };
}

export function eventChannel(subscribe) {
  var buffer = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : buffers.none();
  var matcher = arguments[2];

  /**
    should be if(typeof matcher !== undefined) instead?
    see PR #273 for a background discussion
  **/
  if (arguments.length > 2) {
    check(matcher, is.func, 'Invalid match function passed to eventChannel');
  }

  var chan = channel(buffer);
  var close = function close() {
    if (!chan.__closed__) {
      if (unsubscribe) {
        unsubscribe();
      }
      chan.close();
    }
  };
  var unsubscribe = subscribe(function (input) {
    if (isEnd(input)) {
      close();
      return;
    }
    if (matcher && !matcher(input)) {
      return;
    }
    chan.put(input);
  });
  if (chan.__closed__) {
    unsubscribe();
  }

  if (!is.func(unsubscribe)) {
    throw new Error('in eventChannel: subscribe should return a function to unsubscribe');
  }

  return {
    take: chan.take,
    flush: chan.flush,
    close: close
  };
}

export function stdChannel(subscribe) {
  var chan = eventChannel(function (cb) {
    return subscribe(function (input) {
      if (input[SAGA_ACTION]) {
        cb(input);
        return;
      }
      asap(function () {
        return cb(input);
      });
    });
  });

  return _extends({}, chan, {
    take: function take(cb, matcher) {
      if (arguments.length > 1) {
        check(matcher, is.func, "channel.take's matcher argument must be a function");
        cb[MATCH] = matcher;
      }
      chan.take(cb);
    }
  });
}