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Updated/added fundamentals #40
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jasongwartz
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Feb 28, 2018
| @@ -199,7 +199,9 @@ Result: | |||
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| ### Method chaining | |||
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| The methods **map()**, **filter()** and **reduce()** each return a new array. This makes it possible to chain these methods and create a 'pipeline' of operations, to be applied in sequence. Let's take the last example, but now filtering out only those array elements for which the name starts with a 'J': | |||
| The methods **map()** and **filter()** each return a new array. This makes it possible to chain these methods and create a 'pipeline' of operations, to be applied in sequence. The **reduce** method can return anything, including an array. If a **reduce** method returns something other than an array it can only be included at the end of an array method chain. | |||
fundamentals/promises.md
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| @@ -70,44 +81,61 @@ If you are only interested in the error case, you can pass `null` for the first | |||
| somePromise.then(null, onRejected) | |||
| ``` | |||
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| or you can use a second method exposed by a promise object, which is just a short-hand for calling `then()` with `null` as its first argument: | |||
| or you can use a second method exposed by a promise, which is just a short-hand for calling `then()` with `null` as its first argument: | |||
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Good point here. I also find this line a bit confusing, especially if you didn't know the details of how then() works, might be worth further clarifying how catch() is used in combination with then().
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I've added a .then() before the .catch() in the code snippet. Further down there is an explanation why .catch() should be at the end of the chain, but I realise at this point in the text it remains a bit vague.
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Made a tiny change to clarify that sentence: fa0387b |
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Maybe clarify that Promise.reject(new Error('bad')).catch(() => 'good').then(console.log);
// outputs 'good' |
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I have added a fundamental on the Event Loop and extended the promises fundamental. A minor correction to the map & filter fundamental, in that
reducedoes not return an array by default.In JS3, Week 9 I have interpreted the topic of 'Code Flow' as an explanation of the Event Loop, hence the added fundamental. Please comment if you are of a different opinion.
As promises and the Event Loop are complicated subjects to explain I would really appreciate a critical review of these fundamentals.