gecko-dev/browser/devtools/shared/Promise.jsm
2012-03-14 18:17:43 +01:00

410 lines
10 KiB
JavaScript

/*
* Copyright 2009-2011 Mozilla Foundation and contributors
* Licensed under the New BSD license. See LICENSE.txt or:
* http://opensource.org/licenses/BSD-3-Clause
*/
var EXPORTED_SYMBOLS = [ "Promise" ];
/**
* Create an unfulfilled promise
*
* @param {*=} aTrace A debugging value
*
* @constructor
*/
function Promise(aTrace) {
this._status = Promise.PENDING;
this._value = undefined;
this._onSuccessHandlers = [];
this._onErrorHandlers = [];
this._trace = aTrace;
// Debugging help
if (Promise.Debug._debug) {
this._id = Promise.Debug._nextId++;
Promise.Debug._outstanding[this._id] = this;
}
}
/**
* Debugging options and tools.
*/
Promise.Debug = {
/**
* Set current debugging mode.
*
* @param {boolean} value If |true|, maintain _nextId, _outstanding, _recent.
* Otherwise, cleanup debugging data.
*/
setDebug: function(value) {
Promise.Debug._debug = value;
if (!value) {
Promise.Debug._outstanding = [];
Promise.Debug._recent = [];
}
},
_debug: false,
/**
* We give promises and ID so we can track which are outstanding.
*/
_nextId: 0,
/**
* Outstanding promises. Handy for debugging (only).
*/
_outstanding: [],
/**
* Recently resolved promises. Also for debugging only.
*/
_recent: []
};
/**
* A promise can be in one of 2 states.
* The ERROR and SUCCESS states are terminal, the PENDING state is the only
* start state.
*/
Promise.ERROR = -1;
Promise.PENDING = 0;
Promise.SUCCESS = 1;
/**
* Yeay for RTTI
*/
Promise.prototype.isPromise = true;
/**
* Have we either been resolve()ed or reject()ed?
*/
Promise.prototype.isComplete = function() {
return this._status != Promise.PENDING;
};
/**
* Have we resolve()ed?
*/
Promise.prototype.isResolved = function() {
return this._status == Promise.SUCCESS;
};
/**
* Have we reject()ed?
*/
Promise.prototype.isRejected = function() {
return this._status == Promise.ERROR;
};
/**
* Take the specified action of fulfillment of a promise, and (optionally)
* a different action on promise rejection
*/
Promise.prototype.then = function(onSuccess, onError) {
if (typeof onSuccess === 'function') {
if (this._status === Promise.SUCCESS) {
onSuccess.call(null, this._value);
}
else if (this._status === Promise.PENDING) {
this._onSuccessHandlers.push(onSuccess);
}
}
if (typeof onError === 'function') {
if (this._status === Promise.ERROR) {
onError.call(null, this._value);
}
else if (this._status === Promise.PENDING) {
this._onErrorHandlers.push(onError);
}
}
return this;
};
/**
* Like then() except that rather than returning <tt>this</tt> we return
* a promise which resolves when the original promise resolves
*/
Promise.prototype.chainPromise = function(onSuccess) {
var chain = new Promise();
chain._chainedFrom = this;
this.then(function(data) {
try {
chain.resolve(onSuccess(data));
}
catch (ex) {
chain.reject(ex);
}
}, function(ex) {
chain.reject(ex);
});
return chain;
};
/**
* Supply the fulfillment of a promise
*/
Promise.prototype.resolve = function(data) {
return this._complete(this._onSuccessHandlers,
Promise.SUCCESS, data, 'resolve');
};
/**
* Renege on a promise
*/
Promise.prototype.reject = function(data) {
return this._complete(this._onErrorHandlers, Promise.ERROR, data, 'reject');
};
/**
* Internal method to be called on resolve() or reject()
* @private
*/
Promise.prototype._complete = function(list, status, data, name) {
// Complain if we've already been completed
if (this._status != Promise.PENDING) {
Promise._error("Promise complete.", "Attempted ", name, "() with ", data);
Promise._error("Previous status: ", this._status, ", value =", this._value);
throw new Error('Promise already complete');
}
if (list.length == 0 && status == Promise.ERROR) {
var frame;
var text;
//Complain if a rejection is ignored
//(this is the equivalent of an empty catch-all clause)
Promise._error("Promise rejection ignored and silently dropped", data);
if (data.stack) {// This looks like an exception. Try harder to display it
if (data.fileName && data.lineNumber) {
Promise._error("Error originating at", data.fileName,
", line", data.lineNumber );
}
try {
for (frame = data.stack; frame; frame = frame.caller) {
text += frame + "\n";
}
Promise._error("Attempting to extract exception stack", text);
} catch (x) {
Promise._error("Could not extract exception stack.");
}
} else {
Promise._error("Exception stack not available.");
}
if (Components && Components.stack) {
try {
text = "";
for (frame = Components.stack; frame; frame = frame.caller) {
text += frame + "\n";
}
Promise._error("Attempting to extract current stack", text);
} catch (x) {
Promise._error("Could not extract current stack.");
}
} else {
Promise._error("Current stack not available.");
}
}
this._status = status;
this._value = data;
// Call all the handlers, and then delete them
list.forEach(function(handler) {
handler.call(null, this._value);
}, this);
delete this._onSuccessHandlers;
delete this._onErrorHandlers;
// Remove the given {promise} from the _outstanding list, and add it to the
// _recent list, pruning more than 20 recent promises from that list
delete Promise.Debug._outstanding[this._id];
// The original code includes this very useful debugging aid, however there
// is concern that it will create a memory leak, so we leave it out here.
/*
Promise._recent.push(this);
while (Promise._recent.length > 20) {
Promise._recent.shift();
}
*/
return this;
};
/**
* Log an error on the most appropriate channel.
*
* If the console is available, this method uses |console.warn|. Otherwise,
* this method falls back to |dump|.
*
* @param {...*} items Items to log.
*/
Promise._error = null;
if (typeof console != "undefined" && console.warn) {
Promise._error = function() {
var args = Array.prototype.slice.call(arguments);
args.unshift("Promise");
console.warn.call(console, args);
};
} else {
Promise._error = function() {
var i;
var len = arguments.length;
dump("Promise: ");
for (i = 0; i < len; ++i) {
dump(arguments[i]+" ");
}
dump("\n");
};
}
/**
* Takes an array of promises and returns a promise that that is fulfilled once
* all the promises in the array are fulfilled
* @param promiseList The array of promises
* @return the promise that is fulfilled when all the array is fulfilled
*/
Promise.group = function(promiseList) {
if (!Array.isArray(promiseList)) {
promiseList = Array.prototype.slice.call(arguments);
}
// If the original array has nothing in it, return now to avoid waiting
if (promiseList.length === 0) {
return new Promise().resolve([]);
}
var groupPromise = new Promise();
var results = [];
var fulfilled = 0;
var onSuccessFactory = function(index) {
return function(data) {
results[index] = data;
fulfilled++;
// If the group has already failed, silently drop extra results
if (groupPromise._status !== Promise.ERROR) {
if (fulfilled === promiseList.length) {
groupPromise.resolve(results);
}
}
};
};
promiseList.forEach(function(promise, index) {
var onSuccess = onSuccessFactory(index);
var onError = groupPromise.reject.bind(groupPromise);
promise.then(onSuccess, onError);
});
return groupPromise;
};
/**
* Trap errors.
*
* This function serves as an asynchronous counterpart to |catch|.
*
* Example:
* myPromise.chainPromise(a) //May reject
* .chainPromise(b) //May reject
* .chainPromise(c) //May reject
* .trap(d) //Catch any rejection from a, b or c
* .chainPromise(e) //If either a, b and c or
* //d has resolved, execute
*
* Scenario 1:
* If a, b, c resolve, e is executed as if d had not been added.
*
* Scenario 2:
* If a, b or c rejects, d is executed. If d resolves, we proceed
* with e as if nothing had happened. Otherwise, we proceed with
* the rejection of d.
*
* @param {Function} aTrap Called if |this| promise is rejected,
* with one argument: the rejection.
* @return {Promise} A new promise. This promise resolves if all
* previous promises have resolved or if |aTrap| succeeds.
*/
Promise.prototype.trap = function(aTrap) {
var promise = new Promise();
var resolve = Promise.prototype.resolve.bind(promise);
var reject = function(aRejection) {
try {
//Attempt to handle issue
var result = aTrap.call(aTrap, aRejection);
promise.resolve(result);
} catch (x) {
promise.reject(x);
}
};
this.then(resolve, reject);
return promise;
};
/**
* Execute regardless of errors.
*
* This function serves as an asynchronous counterpart to |finally|.
*
* Example:
* myPromise.chainPromise(a) //May reject
* .chainPromise(b) //May reject
* .chainPromise(c) //May reject
* .always(d) //Executed regardless
* .chainPromise(e)
*
* Whether |a|, |b| or |c| resolve or reject, |d| is executed.
*
* @param {Function} aTrap Called regardless of whether |this|
* succeeds or fails.
* @return {Promise} A new promise. This promise holds the same
* resolution/rejection as |this|.
*/
Promise.prototype.always = function(aTrap) {
var promise = new Promise();
var resolve = function(result) {
try {
aTrap.call(aTrap);
promise.resolve(result);
} catch (x) {
promise.reject(x);
}
};
var reject = function(result) {
try {
aTrap.call(aTrap);
promise.reject(result);
} catch (x) {
promise.reject(result);
}
};
this.then(resolve, reject);
return promise;
};
Promise.prototype.toString = function() {
var status;
switch (this._status) {
case Promise.PENDING:
status = "pending";
break;
case Promise.SUCCESS:
status = "resolved";
break;
case Promise.ERROR:
status = "rejected";
break;
default:
status = "invalid status: "+this._status;
}
return "[Promise " + this._id + " (" + status + ")]";
};