promise.js

/*!
Embeddable Minimum Strictly-Compliant Promises/A+ 1.1.1 Thenable
Copyright (c) 2013-2014 Ralf S. Engelschall (http://engelschall.com)
Licensed under The MIT License (http://opensource.org/licenses/MIT)
*/

'use strict';

/*  promise states [Promises/A+ 2.1]  */
var STATE_PENDING   = 0;                                         /*  [Promises/A+ 2.1.1]  */
var STATE_FULFILLED = 1;                                         /*  [Promises/A+ 2.1.2]  */
var STATE_REJECTED  = 2;                                         /*  [Promises/A+ 2.1.3]  */

/*  promise object constructor  */
var api = function( executor ){
  /*  optionally support non-constructor/plain-function call  */
  if( !(this instanceof api) )
    return new api( executor );

  /*  initialize object  */
  this.id           = 'Thenable/1.0.7';
  this.state        = STATE_PENDING; /*  initial state  */
  this.fulfillValue = undefined;     /*  initial value  */     /*  [Promises/A+ 1.3, 2.1.2.2]  */
  this.rejectReason = undefined;     /*  initial reason */     /*  [Promises/A+ 1.5, 2.1.3.2]  */
  this.onFulfilled  = [];            /*  initial handlers  */
  this.onRejected   = [];            /*  initial handlers  */

  /*  provide optional information-hiding proxy  */
  this.proxy = {
    then: this.then.bind( this )
  };

  /*  support optional executor function  */
  if( typeof executor === 'function' )
    executor.call( this, this.fulfill.bind( this ), this.reject.bind( this ) );
};

/*  promise API methods  */
api.prototype = {
  /*  promise resolving methods  */
  fulfill: function( value ){ return deliver( this, STATE_FULFILLED, 'fulfillValue', value ); },
  reject:  function( value ){ return deliver( this, STATE_REJECTED,  'rejectReason', value ); },

  /*  "The then Method" [Promises/A+ 1.1, 1.2, 2.2]  */
  then: function( onFulfilled, onRejected ){
    var curr = this;
    var next = new api();                                    /*  [Promises/A+ 2.2.7]  */
    curr.onFulfilled.push(
      resolver( onFulfilled, next, 'fulfill' ) );             /*  [Promises/A+ 2.2.2/2.2.6]  */
    curr.onRejected.push(
      resolver( onRejected,  next, 'reject' ) );             /*  [Promises/A+ 2.2.3/2.2.6]  */
    execute( curr );
    return next.proxy;                                       /*  [Promises/A+ 2.2.7, 3.3]  */
  }
};

/*  deliver an action  */
var deliver = function( curr, state, name, value ){
  if( curr.state === STATE_PENDING ){
    curr.state = state;                                      /*  [Promises/A+ 2.1.2.1, 2.1.3.1]  */
    curr[ name ] = value;                                      /*  [Promises/A+ 2.1.2.2, 2.1.3.2]  */
    execute( curr );
  }
  return curr;
};

/*  execute all handlers  */
var execute = function( curr ){
  if( curr.state === STATE_FULFILLED )
    execute_handlers( curr, 'onFulfilled', curr.fulfillValue );
  else if( curr.state === STATE_REJECTED )
    execute_handlers( curr, 'onRejected',  curr.rejectReason );
};

/*  execute particular set of handlers  */
var execute_handlers = function( curr, name, value ){
  /* global setImmediate: true */
  /* global setTimeout: true */

  /*  short-circuit processing  */
  if( curr[ name ].length === 0 )
    return;

  /*  iterate over all handlers, exactly once  */
  var handlers = curr[ name ];
  curr[ name ] = [];                                             /*  [Promises/A+ 2.2.2.3, 2.2.3.3]  */
  var func = function(){
    for( var i = 0; i < handlers.length; i++ )
      handlers[ i ]( value );                                  /*  [Promises/A+ 2.2.5]  */
  };

  /*  execute procedure asynchronously  */                     /*  [Promises/A+ 2.2.4, 3.1]  */
  if( typeof setImmediate === 'function' )
    setImmediate( func );
  else
    setTimeout( func, 0 );
};

/*  generate a resolver function  */
var resolver = function( cb, next, method ){
  return function( value ){
    if( typeof cb !== 'function' )                            /*  [Promises/A+ 2.2.1, 2.2.7.3, 2.2.7.4]  */
      next[ method ].call( next, value );                      /*  [Promises/A+ 2.2.7.3, 2.2.7.4]  */
    else {
      var result;
      try { result = cb( value ); }                          /*  [Promises/A+ 2.2.2.1, 2.2.3.1, 2.2.5, 3.2]  */
      catch( e ){
        next.reject( e );                                  /*  [Promises/A+ 2.2.7.2]  */
        return;
      }
      resolve( next, result );                               /*  [Promises/A+ 2.2.7.1]  */
    }
  };
};

/*  "Promise Resolution Procedure"  */                           /*  [Promises/A+ 2.3]  */
var resolve = function( promise, x ){
  /*  sanity check arguments  */                               /*  [Promises/A+ 2.3.1]  */
  if( promise === x || promise.proxy === x ){
    promise.reject( new TypeError( 'cannot resolve promise with itself' ) );
    return;
  }

  /*  surgically check for a "then" method
    (mainly to just call the "getter" of "then" only once)  */
  var then;
  if( (typeof x === 'object' && x !== null) || typeof x === 'function' ){
    try { then = x.then; }                                   /*  [Promises/A+ 2.3.3.1, 3.5]  */
    catch( e ){
      promise.reject( e );                                   /*  [Promises/A+ 2.3.3.2]  */
      return;
    }
  }

  /*  handle own Thenables    [Promises/A+ 2.3.2]
    and similar "thenables" [Promises/A+ 2.3.3]  */
  if( typeof then === 'function' ){
    var resolved = false;
    try {
      /*  call retrieved "then" method */                  /*  [Promises/A+ 2.3.3.3]  */
      then.call( x,
        /*  resolvePromise  */                           /*  [Promises/A+ 2.3.3.3.1]  */
        function( y ){
          if( resolved ) return; resolved = true;       /*  [Promises/A+ 2.3.3.3.3]  */
          if( y === x )                                 /*  [Promises/A+ 3.6]  */
            promise.reject( new TypeError( 'circular thenable chain' ) );
          else
            resolve( promise, y );
        },

        /*  rejectPromise  */                            /*  [Promises/A+ 2.3.3.3.2]  */
        function( r ){
          if( resolved ) return; resolved = true;       /*  [Promises/A+ 2.3.3.3.3]  */
          promise.reject( r );
        }
      );
    }
    catch( e ){
      if( !resolved )                                       /*  [Promises/A+ 2.3.3.3.3]  */
        promise.reject( e );                               /*  [Promises/A+ 2.3.3.3.4]  */
    }
    return;
  }

  /*  handle other values  */
  promise.fulfill( x );                                          /*  [Promises/A+ 2.3.4, 2.3.3.4]  */
};

// so we always have Promise.all()
api.all = function( ps ){
  return new api(function( resolveAll, rejectAll ){
    var vals = new Array( ps.length );
    var doneCount = 0;

    var fulfill = function( i, val ){
      vals[ i ] = val;
      doneCount++;

      if( doneCount === ps.length ){
        resolveAll( vals );
      }
    };

    for( var i = 0; i < ps.length; i++ ){
      (function( i ){
        var p = ps[i];
        var isPromise = p != null && p.then != null;

        if( isPromise ){
          p.then( function( val ){
            fulfill( i, val );
          }, function( err ){
            rejectAll( err );
          } );
        } else {
          var val = p;
          fulfill( i, val );
        }
      })( i );
    }

  } );
};

api.resolve = function( val ){
  return new api(function( resolve, reject ){ resolve( val ); });
};

api.reject = function( val ){
  return new api(function( resolve, reject ){ reject( val ); });
};

module.exports = typeof Promise !== 'undefined' ? Promise : api; // eslint-disable-line no-undef