Over the last few weeks Sunil Agarwal (from the SQL Storage Engine team) has posted a great series of blog articles about tempdb and the version store, over on my old stomping ground – the Storage Engine blog. The articles are well worth reading – the links are:
Enjoy!
转载于:https://www.cnblogs.com/Amaranthus/archive/2013/04/11/3014018.html
You Don’t Know JS Yet (book series) - 2nd Edition
全文阅读地址From https://github.com/getify/You-Dont-Know-JS
我的GitHub文件： https://github.com/Li-YangZhong/Kyle_Simpson_You_Don-t_Know_JS_Yet_-Get_Started.git
But let me be clear: I don’t think it’s possible to ever fully know JS. That’s not an achievement to be obtained, but a goal to strive after. You don’t finish knowing everything about JS, you just keep learning more and more as you spend more time with the language. And the deeper you go, the more you revisit what you knew before, and you re-learn it from that more experienced perspective.
I encourage you to adopt a mindset around JavaScript, and indeed all of software development, that you will never fully have mastered it, but that you can and should keep working to get closer to that end, a journey that will stretch for the entirety of your software development career, and beyond.From https://github.com/getify/You-Dont-Know-JS/blob/2nd-ed/preface.md
It is not my intention that YDKJSY be read straight through. The material in these books is dense, because JavaScript is powerful, sophisticated, and in parts rather complex. Nobody can really hope to download all this information to their brains in a single pass and retain any significant amount of it. That’s unreasonable, and it’s foolish to try.
From https://github.com/getify/You-Dont-Know-JS/blob/2nd-ed/preface.md
So, do your future self a favor and dig into this book and unlock the knowledge within. These solid foundations will serve you better than any framework ever will; those come and go but we’ll still be writing JavaScript itself for decades to come. Keep an open mind and challenge your preconceived notions.
Don’t buy the lie that you should only learn and use a small collection of good parts while avoiding all the bad stuff. Don’t buy the “X is the new Y” snake oil, that some new feature of the language instantly relegates all usage of a previous feature as obsolete and ignorant. Don’t listen when someone says your code isn’t “modern” because it isn’t yet using a stage-0 feature that was only proposed a few weeks ago!
Every part of JS is useful. Some parts are more useful than others. Some parts require you to be more careful and intentional.
The primary point of the title “You Don’t Know JS Yet” is to point out that most JS developers don’t take the time to really understand how the code that they write works. They know that it works—that it produces a desired outcome. But they either don’t understand exactly how, or worse, they have an inaccurate mental model for the how that falters on closer scrutiny.
In particular, Chapter 4 identifies three main pillars around which the JS language is organized: scope/closures, prototypes/objects, and types/coercion. JS is a broad and sophisticated language, with many features and capabilities. But all of JS is founded on these three foundational pillars.
Further distancing the language from the Oracle-owned trademark, the official name of the language specified by TC39 and formalized by the ECMA standards body is ECMAScript. And indeed, since 2016, the official language name has also been suffixed by the revision year; as of this writing, that’s ECMAScript 2019, or otherwise abbreviated ES2019.
In other words, the JavaScript/JS that runs in your browser or in Node.js, is an implementation of the ES2019 standard.
One of the most foundational principles that guides JavaScript is preservation of backwards compatibility.
Backwards compatibility means that once something is accepted as valid JS, there will not be a future change to the language that causes that code to become invalid JS. Code written in 1995—however primitive or limited it may have been!—should still work today. As TC39 members often proclaim, “we don’t break the web!”
The idea is that JS developers can write code with confidence that their code won’t stop working unpredictably because a browser update is released. This makes the decision to choose JS for a program a more wise and safe investment, for years into the future.
Always write code using the most appropriate features to communicate its ideas and intent effectively. In general, this means using the most recent stable JS version. Avoid negatively impacting the code’s readability by trying to manually adjust for the syntax/API gaps. That’s what tools are for!
JS source code is parsed before it is executed.
What does the name pragma mean?
In plain English, pragmatic is an adjective that means sensible and practical. In programming, pragma refers to: The code that consists of useful information on how a compiler or interpreter or assembler should process the program. pragma does not contribute anything to the programming language itself.*
Strict mode is switched on per file with a special pragma (nothing allowed before it except comments/whitespace):
// only whitespace and comments are allowed // before the use-strict pragma "use strict"; // the rest of the file runs in strict mode*
Strict mode can alternatively be turned on per-function scope, with exactly the same rules about its surroundings:
function someOperations() { // whitespace and comments are fine here "use strict"; // all this code will run in strict mode }Interestingly, if a file has strict mode turned on, the function-level strict mode pragmas are disallowed. So you have to pick one or the other.
ES6 modules assume strict mode, so all code in such files is automatically defaulted to strict mode.
Further reading on strict mode https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode
JS is a compiled language, meaning the tools (including the JS engine) process and verify a program (reporting any errors!) before it executes.
In JS, each standalone file is its own separate program. The reason this matters is primarily around error handling. Since JS treats files as programs, one file may fail (during parse/compile or execution) and that will not necessarily prevent the next file from being processed.
Strings are ordered collections of characters, usually used to represent words and sentences.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules
Always keep looking for better ways to use what JS gives us to author more readable code.
From https://github.com/getify/You-Dont-Know-JS/blob/2nd-ed/get-started/ch4.md
(This article was first published on Plotly Blog, and kindly contributed to R-bloggers) Many graphs use a time series, meaning they measure events over time. William Playfair (1759 - 1823) was a Scottish economist and pioneer of this approach. Playfair invented the line graph. The graph below–one of his most famous–depicts how in the 1750s the Brits started exporting more than they were importing.This post shows how you can use Playfair’s approach and many more for making a time series graph. To embed Plotly graphs in your applications, dashboards, and reports, check out Plotly Enterprise.
1. By Year
First we’ll show an example of a standard time series graph. The data is drawn from a paper on shaving trends. The author concludes that the “dynamics of taste”, in this case facial hair, are “common expressions of underlying conditions and sequences in social behavior.” Time is on the x-axis. The y-axis shows the respective percentages of men’s facial hair styles.width="900" id="plotly-Dreamshot:1452" src="https://plot.ly/~Dreamshot/1452.embed" frameborder="0" scrolling="no" style="visibility: hidden; position: absolute; max-width: 100%;">
You can click and drag to move the axis, click and drag to zoom, or toggle traces on and off in the legend. The temperatue graph below shows how Plotly adjusts data from years to nanoseconds as you zoom. The first timestamp is 2014-12-15 08:55:13.961347, which is how Plotly reads dates. That is, `yyyy-mm-dd HH:MM:SS.ssssss`. Now that’s drilling down.
One of the special things about Plotly is that you can translate plots and data between programming lanuguages, file formats, and data types. For example, the multiple axis plot below uses stacked plots on the same time scale for different eonomic indicators. This plot was made using ggplot2’s time scale. We can convert the plot into Plotly, allowing anyone to edit the figure from different programming languages or the Plotly web app.width="1189" id="plotly-MattSundquist:10864" src="https://plot.ly/~MattSundquist/10864.embed" frameborder="0" scrolling="no" style="visibility: hidden; position: absolute; max-width: 100%;">
We have a time series tutorial that explains time series graphs, custom date formats, custom hover text labels, and time series plots in MATLAB, Python, and R.2. Subplots & Small Multiples
Another way to slice your data is by subplots. These histograms were made with R and compare yearly data. Each plot shows the annual number of players who had a given batting average in Major League Baseball.width="1189" id="plotly-MattSundquist:11035" src="https://plot.ly/~MattSundquist/11035.embed" frameborder="0" scrolling="no" style="visibility: hidden; position: absolute; max-width: 100%;">
You can also display your data using small multiples, a concept developed by Edward Tufte. Small multiples are “illustrations of postage-stamp” size. They use the same graph type to index data by a cateogry or label. Using facets, we’ve plotted a dataset of airline passengers. Each subplot shows the overall travel numbers and a reference line for the thousands of passengers travelling that month.width="1189" id="plotly-MattSundquist:10875" src="https://plot.ly/~MattSundquist/10875.embed" frameborder="0" scrolling="no" style="visibility: hidden; position: absolute; max-width: 100%;">
3. By Month
The heatmap below shows the percentages of people’s birthdays on a given date, gleaned from 480,040 life isurance applications. The x-axis shows months, the y-axis shows the day of the month, and the z shows the % of birthdays on each date.width="750" id="plotly-Dreamshot:354" src="https://plot.ly/~Dreamshot/354.embed" frameborder="0" scrolling="no" style="visibility: hidden; position: absolute; max-width: 100%;">
To show how values in your data are spaced over different months, we can use seasonal boxplots. The boxes represent how the data is spaced for each month; the dots represent outliers. We’ve used ggplot2 to make our plot and added a smoothed fit with a confidence interval. See our box plot tutorial to learn more.width="829" id="plotly-MattSundquist:10984" src="https://plot.ly/~MattSundquist/10984.embed" frameborder="0" scrolling="no" style="visibility: hidden; position: absolute; max-width: 100%;">
We can use a bar chart with error bars to look at data over a monthly interval. In this case, we’re using R to make a graph with error bars showing snowfall in Montreal.id="plotly-chelsea_lyn:158" src="https://plot.ly/~chelsea_lyn/158.embed" frameborder="0" scrolling="no" style="visibility: hidden; position: absolute; max-width: 100%;">
4. A Repeated Event With A Category
We may want to look at data that is not stricly a time series plot, but still represents changes over time. For example, we may want hourly event data. Below we’re showing the most popular hourly reasons to call 311 in NYC, a number you can call for non-emergency help. The plot is from our pandas and SQLite guide.width="808" id="plotly-MattSundquist:10789" src="https://plot.ly/~MattSundquist/10789.embed" frameborder="0" scrolling="no" style="visibility: hidden; position: absolute; max-width: 100%;">
We can also show a before and after effect to examine changes from an event. The plot below, made in an IPython Notebook, tracks Conservative and Labour election impacts on Pounds and Dollars.width="800" id="plotly-MattSundquist:11482" src="https://plot.ly/~MattSundquist/11482.embed" frameborder="0" scrolling="no" style="visibility: hidden; position: absolute; max-width: 100%;">
5. A 3D Graph
We can also use a 3D chart to show events over time. For example, our surface chart below shows the UK Swaps Term Structure with historical dates along the X axis, the Term Structure on the Y axis, and the swap rates over the Z Axis. The message: rates are lower than ever. At the long end of the curve we don’t see a massive increase. This example was made using cufflinks, a Python library by Jorge Santos. For more on 3D graphing see our Python, MATLAB, R, and web tutorials.width="685" id="plotly-MattSundquist:11399" src="https://plot.ly/~MattSundquist/11399.embed" frameborder="0" scrolling="no" style="visibility: hidden; position: absolute; max-width: 100%;">
Sharing & Deploying Plotly
If you liked this post, please consider sharing. We’re @plotlygraphs, or email us at feedback at plot dot ly. We have tutorials that show how to make and embed graphs in your website, blog, or apps. To learn more about how companies are using Plotly Enterprise across different industries, see our customer stories.
As the nerve of the whole network deployment, data switch can provide high performance and density to ensure the normal operation of all connections. The smart switch of Cisco has gained great popularity among engineers. in February, 2017, Cisco has announced the significant advancements and enhancements to the Cisco Nexus 9000 portfolio. Have you upgraded to Cisco Nexus 9000 Series switches? This article will guide you to have a close look at Cisco Nexus 9000.
Overview of Cisco Nexus 9000Cisco Nexus 9000 Series delivers proven high performance and density, low latency, and exceptional power efficiency in a range of form factors. The switches operate in Cisco NX-OS Software or Application Centric Infrastructure (ACI) modes with ground-breaking Cloud Scale ASIC technology. They are ideal for traditional or fully automated data center deployments. Here is figure of Cisco Nexus 9000 Series switches.
Shining Points of Cisco Nexus 9000Many experts said that the Cisco Nexus 9000 Series is the right choice as the foundation for today’s hybrid enterprise data centers. Why? This part will show you the shining points of Cisco Nexus 9000.
The Cisco Nexus 9000 Series provides multiyear, sustained differentiation between Cisco and point-product network providers and providers of proprietary, single-vendor public clouds, supporting greater performance and enhanced operations through features including intelligent services, programmability, automation, analytics, and manageability. If you want to get higher performance of your network deployment, it is time to upgrade to Cisco Nexus 9000.
