Async patterns: Promises

Given our understanding of what async is, how the callback pattern manages async, and some of the deficiencies of the callback pattern, let’s dive into another, newer pattern — promises.

Promises are clearly exciting the JS community. As someone who never really knew JavaScript before promises, I have only an academic understanding of the magnitude of this shift. In fact, I think I was exposed to management of async first with callbacks to make promises seem just that much more awesome (like building a node server before meeting Express). Understanding both is important to a deeper understanding of each, individually.

As with callbacks, for a new developer, it can be difficult to sift through the massive amount of information available online. For the benefit of anyone else newly exposed to promises, in this post I’ve attempted to cull the resources and posts that I have found most enlightening through my own learning.

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Async patterns: Callbacks

So what is a callback function?

A callback function, also known as a higher-order function, is a function that is passed to another function (let’s call this other function “otherFunction”) as a parameter, and the callback function is called (or executed) inside the otherFunction. A callback function is essentially a pattern (an established solution to a common problem), and therefore, the use of a callback function is also known as a callback pattern. (Source)

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What is asynchronous JavaScript?

When people talk about asynchrony in JavaScript, what do they mean? First, a real-world example of an asynchronous process (summarized here, and originally here).

Imagine you walk into a coffee shop to get a latte. If they’re busy, perhaps you wait in line. When it’s your turn, you place your order with the cashier, and pay for the drink. The cashier writes your order — maybe even your name — on a coffee cup, and places it behind the empty (not yet fulfilled) cup of the person who ordered before you. Perhaps the shop is quite busy and there are ten cups ahead of yours. That queue of yet-unfilled coffee cups allows for the separation of the cashier (processing and queuing orders) and the barista (fulfilling orders based on the information supplied by the cashier). This queuing process results in increased efficiency and output. (The original source expands on the metaphor and is quite interesting). This is an example of asynchronous, non-blocking behavior.

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Let’s learn the Dvorak keyboard

In the last week, the subject of the Dvorak keyboard has come up more than usual. (‘Usual’ being not at all.) The Dvorak keyboard is an alternative to the widely-adopted QWERTY keyboard, and was patented in 1936 by Dr. August Dvorak and his brother-in-law, Dr. William Dealey. There are a couple of devotees among my coworkers at MakerSquare, and at some point in one of our discussions, I became inspired — how quickly could I pick it up? Or further, how long would it take to achieve at least half of my QWERTY speed? So I tested, to get my baseline, coming in at 120 WPM.

Screen Shot 2016-06-04 at 11.01.18 AM

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