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Improves implementing page readability #37

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Improves implementing page readability #37

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dfbfc01
Adds whole implementation code at the end of the page
alexbonhomme Dec 25, 2015
7b5c72e
Split .done part explanations to be more clear about handlers
alexbonhomme Dec 25, 2015
dda7f73
Fix potential null pointer on handlers queue
alexbonhomme Dec 25, 2015
890d4bb
Improves consistency by renaming 'ex' exception variables
alexbonhomme Dec 25, 2015
e9d76e2
Fix comments and put chapter title before whole implementation code
alexbonhomme Dec 25, 2015
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156 changes: 118 additions & 38 deletions views/implementing.jade
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Original file line number Diff line number Diff line change
Expand Up @@ -154,10 +154,10 @@ block content
done = true
onRejected(reason)
})
} catch (ex) {
} catch (e) {
if (done) return
done = true
onRejected(ex)
onRejected(e)
}
}

Expand Down Expand Up @@ -231,6 +231,92 @@ block content
li it is never called until the next tick (i.e. after the #[code .done] method has returned)
li it is called regardless of whether the promise is resolved before or after we call #[code .done]

:js
// manages handlers according to Promise state
function handle(handler) {
if (state === PENDING) {
handlers.push(handler);
} else {
if (state === FULFILLED &&
typeof handler.onFulfilled === 'function') {
handler.onFulfilled(value);
}
if (state === REJECTED &&
typeof handler.onRejected === 'function') {
handler.onRejected(value);
}
}
}

this.done = function (onFulfilled, onRejected) {
// ensure we are always asynchronous
setTimeout(function () {
handle({
onFulfilled: onFulfilled,
onRejected: onRejected
});
}, 0);
}

p.
We make sure to notify the handlers when the Promise is resolved or rejected.
We only ever do this in the next tick by removes them from the queue.

:js
function fulfill(result) {
state = FULFILLED;
value = result;

// runs handlers and resets queue
handlers.forEach(handle);
handlers = [];
}

function reject(error) {
state = REJECTED;
value = error;

// runs handlers and resets queue
handlers.forEach(handle);
handlers = [];
}

h2#then Observing (via .then)

p.
Now that we have #[code .done] implemented, we can easily implement #[code .then] to
just do the same thing, but construct a new Promise in the process.

:js
this.then = function (onFulfilled, onRejected) {
var self = this;
return new Promise(function (resolve, reject) {
return self.done(function (result) {
if (typeof onFulfilled === 'function') {
try {
return resolve(onFulfilled(result));
} catch (e) {
return reject(e);
}
} else {
return resolve(result);
}
}, function (error) {
if (typeof onRejected === 'function') {
try {
return resolve(onRejected(error));
} catch (e) {
return reject(e);
}
} else {
return reject(error);
}
});
});
}

h2#allcode The whole implementation

:js
var PENDING = 0;
var FULFILLED = 1;
Expand All @@ -249,13 +335,17 @@ block content
function fulfill(result) {
state = FULFILLED;
value = result;

// runs handlers and resets queue
handlers.forEach(handle);
handlers = null;
}

function reject(error) {
state = REJECTED;
value = error;

// runs handlers and resets queue
handlers.forEach(handle);
handlers = null;
}
Expand All @@ -273,6 +363,7 @@ block content
}
}

// manages handlers according to Promise state
function handle(handler) {
if (state === PENDING) {
handlers.push(handler);
Expand All @@ -298,45 +389,34 @@ block content
}, 0);
}

doResolve(fn, resolve, reject);
}

p.
We make sure to notify the handlers when the Promise is resolved or rejected.
We only ever do this in the next tick.

h2#then Observing (via .then)

p.
Now that we have #[code .done] implemented, we can easily implement #[code .then] to
just do the same thing, but construct a new Promise in the process.

:js
this.then = function (onFulfilled, onRejected) {
var self = this;
return new Promise(function (resolve, reject) {
return self.done(function (result) {
if (typeof onFulfilled === 'function') {
try {
return resolve(onFulfilled(result));
} catch (ex) {
return reject(ex);
this.then = function (onFulfilled, onRejected) {
var self = this;
return new Promise(function (resolve, reject) {
return self.done(function (result) {
if (typeof onFulfilled === 'function') {
try {
return resolve(onFulfilled(result));
} catch (e) {
return reject(e);
}
} else {
return resolve(result);
}
} else {
return resolve(result);
}
}, function (error) {
if (typeof onRejected === 'function') {
try {
return resolve(onRejected(error));
} catch (ex) {
return reject(ex);
}, function (error) {
if (typeof onRejected === 'function') {
try {
return resolve(onRejected(error));
} catch (e) {
return reject(e);
}
} else {
return reject(error);
}
} else {
return reject(error);
}
});
});
});
}

doResolve(fn, resolve, reject);
}

h2#apendix Further Reading
Expand Down