index.js

/* jshint node: true */
"use strict";

function makeArrayFrom(obj) {
  return Array.prototype.slice.apply(obj);
}

var
  PENDING = "pending",
  RESOLVED = "resolved",
  REJECTED = "rejected";

function SynchronousPromise(handler) {
  this.status = PENDING;
  this._continuations = [];
  this._parent = null;
  this._paused = false;
  if (handler) {
    handler.call(
      this,
      this._continueWith.bind(this),
      this._failWith.bind(this)
    );
  }
}

function looksLikeAPromise(obj) {
  return obj && typeof (obj.then) === "function";
}

function passThrough(value) {
  return value;
}

SynchronousPromise.prototype = {
  then: function (nextFn, catchFn) {
    var next = SynchronousPromise.unresolved()._setParent(this);
    if (this._isRejected()) {
      if (this._paused) {
        this._continuations.push({
          promise: next,
          nextFn: nextFn,
          catchFn: catchFn
        });
        return next;
      }
      if (catchFn) {
        try {
          var catchResult = catchFn(this._error);
          if (looksLikeAPromise(catchResult)) {
            this._chainPromiseData(catchResult, next);
            return next;
          } else {
            return SynchronousPromise.resolve(catchResult)._setParent(this);
          }
        } catch (e) {
          return SynchronousPromise.reject(e)._setParent(this);
        }
      }
      return SynchronousPromise.reject(this._error)._setParent(this);
    }
    this._continuations.push({
      promise: next,
      nextFn: nextFn,
      catchFn: catchFn
    });
    this._runResolutions();
    return next;
  },
  catch: function (handler) {
    if (this._isResolved()) {
      return SynchronousPromise.resolve(this._data)._setParent(this);
    }
    var next = SynchronousPromise.unresolved()._setParent(this);
    this._continuations.push({
      promise: next,
      catchFn: handler
    });
    this._runRejections();
    return next;
  },
  finally: function (callback) {
    var ran = false;

    function runFinally(result, err) {
      if (!ran) {
        ran = true;
        if (!callback) {
          callback = passThrough;
        }
        var callbackResult = callback(result);
        if (looksLikeAPromise(callbackResult)) {
          return callbackResult.then(function () {
            if (err) {
              throw err;
            }
            return result;
          });
        } else {
          return result;
        }
      }
    }

    return this
      .then(function (result) {
        return runFinally(result);
      })
      .catch(function (err) {
        return runFinally(null, err);
      });
  },
  pause: function () {
    this._paused = true;
    return this;
  },
  resume: function () {
    var firstPaused = this._findFirstPaused();
    if (firstPaused) {
      firstPaused._paused = false;
      firstPaused._runResolutions();
      firstPaused._runRejections();
    }
    return this;
  },
  _findAncestry: function () {
    return this._continuations.reduce(function (acc, cur) {
      if (cur.promise) {
        var node = {
          promise: cur.promise,
          children: cur.promise._findAncestry()
        };
        acc.push(node);
      }
      return acc;
    }, []);
  },
  _setParent: function (parent) {
    if (this._parent) {
      throw new Error("parent already set");
    }
    this._parent = parent;
    return this;
  },
  _continueWith: function (data) {
    var firstPending = this._findFirstPending();
    if (firstPending) {
      firstPending._data = data;
      firstPending._setResolved();
    }
  },
  _findFirstPending: function () {
    return this._findFirstAncestor(function (test) {
      return test._isPending && test._isPending();
    });
  },
  _findFirstPaused: function () {
    return this._findFirstAncestor(function (test) {
      return test._paused;
    });
  },
  _findFirstAncestor: function (matching) {
    var test = this;
    var result;
    while (test) {
      if (matching(test)) {
        result = test;
      }
      test = test._parent;
    }
    return result;
  },
  _failWith: function (error) {
    var firstRejected = this._findFirstPending();
    if (firstRejected) {
      firstRejected._error = error;
      firstRejected._setRejected();
    }
  },
  _takeContinuations: function () {
    return this._continuations.splice(0, this._continuations.length);
  },
  _runRejections: function () {
    if (this._paused || !this._isRejected()) {
      return;
    }
    var
      error = this._error,
      continuations = this._takeContinuations(),
      self = this;
    continuations.forEach(function (cont) {
      if (cont.catchFn) {
        try {
          var catchResult = cont.catchFn(error);
          self._handleUserFunctionResult(catchResult, cont.promise);
        } catch (e) {
          cont.promise.reject(e);
        }
      } else {
        cont.promise.reject(error);
      }
    });
  },
  _runResolutions: function () {
    if (this._paused || !this._isResolved() || this._isPending()) {
      return;
    }
    var continuations = this._takeContinuations();
    var data = this._data;
    var self = this;
    continuations.forEach(function (cont) {
      if (cont.nextFn) {
        try {
          var result = cont.nextFn(data);
          self._handleUserFunctionResult(result, cont.promise);
        } catch (e) {
          self._handleResolutionError(e, cont);
        }
      } else if (cont.promise) {
        cont.promise.resolve(data);
      }
    });
    if (looksLikeAPromise(this._data)) {
      return this._handleWhenResolvedDataIsPromise(this._data);
    }
  },
  _handleResolutionError: function (e, continuation) {
    this._setRejected();
    if (continuation.catchFn) {
      try {
        continuation.catchFn(e);
        return;
      } catch (e2) {
        e = e2;
      }
    }
    if (continuation.promise) {
      continuation.promise.reject(e);
    }
  },
  _handleWhenResolvedDataIsPromise: function (data) {
    var self = this;
    return data.then(function (result) {
      self._data = result;
      self._runResolutions();
    }).catch(function (error) {
      self._error = error;
      self._setRejected();
      self._runRejections();
    });
  },
  _handleUserFunctionResult: function (data, nextSynchronousPromise) {
    if (looksLikeAPromise(data)) {
      this._chainPromiseData(data, nextSynchronousPromise);
    } else {
      nextSynchronousPromise.resolve(data);
    }
  },
  _chainPromiseData: function (promiseData, nextSynchronousPromise) {
    promiseData.then(function (newData) {
      nextSynchronousPromise.resolve(newData);
    }).catch(function (newError) {
      nextSynchronousPromise.reject(newError);
    });
  },
  _setResolved: function () {
    this.status = RESOLVED;
    if (!this._paused) {
      this._runResolutions();
    }
  },
  _setRejected: function () {
    this.status = REJECTED;
    if (!this._paused) {
      this._runRejections();
    }
  },
  _isPending: function () {
    return this.status === PENDING;
  },
  _isResolved: function () {
    return this.status === RESOLVED;
  },
  _isRejected: function () {
    return this.status === REJECTED;
  }
};

SynchronousPromise.resolve = function (result) {
  return new SynchronousPromise(function (resolve, reject) {
    if (looksLikeAPromise(result)) {
      result.then(function (newResult) {
        resolve(newResult);
      }).catch(function (error) {
        reject(error);
      });
    } else {
      resolve(result);
    }
  });
};

SynchronousPromise.reject = function (result) {
  return new SynchronousPromise(function (resolve, reject) {
    reject(result);
  });
};

SynchronousPromise.unresolved = function () {
  return new SynchronousPromise(function (resolve, reject) {
    this.resolve = resolve;
    this.reject = reject;
  });
};

SynchronousPromise.all = function () {
  var args = makeArrayFrom(arguments);
  if (Array.isArray(args[0])) {
    args = args[0];
  }
  if (!args.length) {
    return SynchronousPromise.resolve([]);
  }
  return new SynchronousPromise(function (resolve, reject) {
    var
      allData = [],
      numResolved = 0,
      doResolve = function () {
        if (numResolved === args.length) {
          resolve(allData);
        }
      },
      rejected = false,
      doReject = function (err) {
        if (rejected) {
          return;
        }
        rejected = true;
        reject(err);
      };
    args.forEach(function (arg, idx) {
      SynchronousPromise.resolve(arg).then(function (thisResult) {
        allData[idx] = thisResult;
        numResolved += 1;
        doResolve();
      }).catch(function (err) {
        doReject(err);
      });
    });
  });
};

function createAggregateErrorFrom(errors) {
  /* jshint ignore:start */
  if (typeof window !== "undefined" && "AggregateError" in window) {
    return new window.AggregateError(errors);
  }
  /* jshint ignore:end */

  return { errors: errors };
}

SynchronousPromise.any = function () {
  var args = makeArrayFrom(arguments);
  if (Array.isArray(args[0])) {
    args = args[0];
  }
  if (!args.length) {
    return SynchronousPromise.reject(createAggregateErrorFrom([]));
  }
  return new SynchronousPromise(function (resolve, reject) {
    var
      allErrors = [],
      numRejected = 0,
      doReject = function () {
        if (numRejected === args.length) {
          reject(createAggregateErrorFrom(allErrors));
        }
      },
      resolved = false,
      doResolve = function (result) {
        if (resolved) {
          return;
        }
        resolved = true;
        resolve(result);
      };
    args.forEach(function (arg, idx) {
      SynchronousPromise.resolve(arg).then(function (thisResult) {
        doResolve(thisResult);
      }).catch(function (err) {
        allErrors[idx] = err;
        numRejected += 1;
        doReject();
      });
    });
  });
};

SynchronousPromise.allSettled = function () {
  var args = makeArrayFrom(arguments);
  if (Array.isArray(args[0])) {
    args = args[0];
  }
  if (!args.length) {
    return SynchronousPromise.resolve([]);
  }
  return new SynchronousPromise(function (resolve) {
    var
      allData = [],
      numSettled = 0,
      doSettled = function () {
        numSettled += 1;
        if (numSettled === args.length) {
          resolve(allData);
        }
      };
    args.forEach(function (arg, idx) {
      SynchronousPromise.resolve(arg).then(function (thisResult) {
        allData[idx] = {
          status: "fulfilled",
          value: thisResult
        };
        doSettled();
      }).catch(function (err) {
        allData[idx] = {
          status: "rejected",
          reason: err
        };
        doSettled();
      });
    });
  });
};

/* jshint ignore:start */
if (Promise === SynchronousPromise) {
  throw new Error("Please use SynchronousPromise.installGlobally() to install globally");
}
var RealPromise = Promise;
SynchronousPromise.installGlobally = function (__awaiter) {
  if (Promise === SynchronousPromise) {
    return __awaiter;
  }
  var result = patchAwaiterIfRequired(__awaiter);
  Promise = SynchronousPromise;
  return result;
};

SynchronousPromise.uninstallGlobally = function () {
  if (Promise === SynchronousPromise) {
    Promise = RealPromise;
  }
};

function patchAwaiterIfRequired(__awaiter) {
  if (typeof (__awaiter) === "undefined" || __awaiter.__patched) {
    return __awaiter;
  }
  var originalAwaiter = __awaiter;
  __awaiter = function () {
    var Promise = RealPromise;
    originalAwaiter.apply(this, makeArrayFrom(arguments));
  };
  __awaiter.__patched = true;
  return __awaiter;
}

/* jshint ignore:end */

module.exports = {
  SynchronousPromise: SynchronousPromise
};