core.js 4.74 KB
Newer Older
liang ce committed
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213
'use strict';

var asap = require('asap');

function noop() {}

// States:
//
// 0 - pending
// 1 - fulfilled with _value
// 2 - rejected with _value
// 3 - adopted the state of another promise, _value
//
// once the state is no longer pending (0) it is immutable

// All `_` prefixed properties will be reduced to `_{random number}`
// at build time to obfuscate them and discourage their use.
// We don't use symbols or Object.defineProperty to fully hide them
// because the performance isn't good enough.


// to avoid using try/catch inside critical functions, we
// extract them to here.
var LAST_ERROR = null;
var IS_ERROR = {};
function getThen(obj) {
  try {
    return obj.then;
  } catch (ex) {
    LAST_ERROR = ex;
    return IS_ERROR;
  }
}

function tryCallOne(fn, a) {
  try {
    return fn(a);
  } catch (ex) {
    LAST_ERROR = ex;
    return IS_ERROR;
  }
}
function tryCallTwo(fn, a, b) {
  try {
    fn(a, b);
  } catch (ex) {
    LAST_ERROR = ex;
    return IS_ERROR;
  }
}

module.exports = Promise;

function Promise(fn) {
  if (typeof this !== 'object') {
    throw new TypeError('Promises must be constructed via new');
  }
  if (typeof fn !== 'function') {
    throw new TypeError('Promise constructor\'s argument is not a function');
  }
  this._40 = 0;
  this._65 = 0;
  this._55 = null;
  this._72 = null;
  if (fn === noop) return;
  doResolve(fn, this);
}
Promise._37 = null;
Promise._87 = null;
Promise._61 = noop;

Promise.prototype.then = function(onFulfilled, onRejected) {
  if (this.constructor !== Promise) {
    return safeThen(this, onFulfilled, onRejected);
  }
  var res = new Promise(noop);
  handle(this, new Handler(onFulfilled, onRejected, res));
  return res;
};

function safeThen(self, onFulfilled, onRejected) {
  return new self.constructor(function (resolve, reject) {
    var res = new Promise(noop);
    res.then(resolve, reject);
    handle(self, new Handler(onFulfilled, onRejected, res));
  });
}
function handle(self, deferred) {
  while (self._65 === 3) {
    self = self._55;
  }
  if (Promise._37) {
    Promise._37(self);
  }
  if (self._65 === 0) {
    if (self._40 === 0) {
      self._40 = 1;
      self._72 = deferred;
      return;
    }
    if (self._40 === 1) {
      self._40 = 2;
      self._72 = [self._72, deferred];
      return;
    }
    self._72.push(deferred);
    return;
  }
  handleResolved(self, deferred);
}

function handleResolved(self, deferred) {
  asap(function() {
    var cb = self._65 === 1 ? deferred.onFulfilled : deferred.onRejected;
    if (cb === null) {
      if (self._65 === 1) {
        resolve(deferred.promise, self._55);
      } else {
        reject(deferred.promise, self._55);
      }
      return;
    }
    var ret = tryCallOne(cb, self._55);
    if (ret === IS_ERROR) {
      reject(deferred.promise, LAST_ERROR);
    } else {
      resolve(deferred.promise, ret);
    }
  });
}
function resolve(self, newValue) {
  // Promise Resolution Procedure: https://github.com/promises-aplus/promises-spec#the-promise-resolution-procedure
  if (newValue === self) {
    return reject(
      self,
      new TypeError('A promise cannot be resolved with itself.')
    );
  }
  if (
    newValue &&
    (typeof newValue === 'object' || typeof newValue === 'function')
  ) {
    var then = getThen(newValue);
    if (then === IS_ERROR) {
      return reject(self, LAST_ERROR);
    }
    if (
      then === self.then &&
      newValue instanceof Promise
    ) {
      self._65 = 3;
      self._55 = newValue;
      finale(self);
      return;
    } else if (typeof then === 'function') {
      doResolve(then.bind(newValue), self);
      return;
    }
  }
  self._65 = 1;
  self._55 = newValue;
  finale(self);
}

function reject(self, newValue) {
  self._65 = 2;
  self._55 = newValue;
  if (Promise._87) {
    Promise._87(self, newValue);
  }
  finale(self);
}
function finale(self) {
  if (self._40 === 1) {
    handle(self, self._72);
    self._72 = null;
  }
  if (self._40 === 2) {
    for (var i = 0; i < self._72.length; i++) {
      handle(self, self._72[i]);
    }
    self._72 = null;
  }
}

function Handler(onFulfilled, onRejected, promise){
  this.onFulfilled = typeof onFulfilled === 'function' ? onFulfilled : null;
  this.onRejected = typeof onRejected === 'function' ? onRejected : null;
  this.promise = promise;
}

/**
 * Take a potentially misbehaving resolver function and make sure
 * onFulfilled and onRejected are only called once.
 *
 * Makes no guarantees about asynchrony.
 */
function doResolve(fn, promise) {
  var done = false;
  var res = tryCallTwo(fn, function (value) {
    if (done) return;
    done = true;
    resolve(promise, value);
  }, function (reason) {
    if (done) return;
    done = true;
    reject(promise, reason);
  });
  if (!done && res === IS_ERROR) {
    done = true;
    reject(promise, LAST_ERROR);
  }
}