Instructional-Objectives-C4.Doc: Fill & Download for Free

The practical method is as follows:1) As you walk up to the line observe which ones are using a magnetometer (metal detector) if at all possible get in to that line.2) If you can, ask security if we are removing shoes today (this varies from country to country and sometimes month to month - security pretends to follow a consistent protocol but that just ain't so).3) While waiting in line remove any metal objects (e.g. keys, wallet of coins, beltbuckles) and place them in your jacket or whatever bag you are carrying - anything you aren't going to take through the magnetometer. I usually do not remove my wedding ring but more on that later.4) With one action pick up 4 trays, and drop them from the bottom of your stack one by one like you are laying plates. Leave space between the first 2 and the last two (this is for your roll aboard).5) Place your items on the belt in the following order-Shoes (if you need to take them off)-Jacket-Roll aboard-Computer bag-Computer5) Wait to be asked through the magnetometer (remember I said always pick the line with the metal detector if you can - not the slow and quite frankly useless nude body scanners). When asked walk through as close to the center as possible, keep hands in the center of the body - if you wear a ring the center of the magnetometer is the least sensitive place and is unlikely to cause an alarm.6) When you get to the other side your items should come out in optimal order. Put your shoes and jacket on first.7) Place your roller aboard on the ground and your computer bag on top of this.8) The computer takes longest to screen so you should have had plenty of time to get organised and all you need to do is place the computer in your computer bag that is sitting on the roll aboard and can walk off.9) Write to your congressman. We’d get a lot more speed if everyone who read this answer would, right now, write a three sentence email to their congressman saying:"Please get rid of the pointless and wasteful TSA. As a brave American I don't need a false sense of security and I'd like you to spend the money instead on schools, roads, and libraries. Passengers have proven they will take care of themselves much better than the guys with rubber gloves ever will, thank you very much."At a minimum we'd get some movement in the right direction and writing to congress en mass does work. To find your representative look at:https://www.house.gov/representatives/find-your-representativeA little bit more detail for those who want to write at length:https://www.thoughtco.com/write-effective-letters-to-congress-3322301Couple of Notes==============Note I didn't say remove liquids and gels. Now, I would never advocate deliberately attempting to evade detection or deliberately leaving this stuff in there - you should dump it before getting to the airport. But the reality is that I've forgotten that stuff in with my computer cables so many times I know that they basically rarely ever find it. Once I was drinking a half gallon sized bottle of milk on my way to the airport, got busy and distracted when I got there forgot about it in my computer bag and it sailed through. Once I left a quart sized bottle of shampoo in there by mistake again my bag has sailed through. So don't waste your time searching your bag for it.I spent my PhD and post-doc designing scanners that while not identical to airport security systems are closely related. So, try not to snigger too much when the TSA uses a "magic" machine that purportedly detects explosives, dangerous liquids or unicorns. I’ll leave you to search the internet for stories from people who after tours in Iraq had visible explosive residue on the exterior of their bags that didn’t set of any alarms from the “magic” machine. If you think that such "magic" machines actually work on a consistent basis I have an investment opportunity in Nigeria for you.Remember the TSA's own tests show that 95% of the time they can not find contraband (see TSA's 95% failure rate shows airport security is a charade - Los Angeles Times). Don't waste your time searching your bag for it - the TSA probably will not find it. The above instructions are optimized for what the airport security can find. For example they can easily figure out if you are wearing shoes and so might ask you to take them off - the fact that they can't tell if the shoes are made of C4 or swiss cheese is obviously irrelevant to them. They can figure out if you are wearing a jacket so might ask you to take it off, however they will never figure out if that jacket is made of gun-cotton. They can easily find a metal object bigger than a wedding ring on your person. Trying to detect pretty much anything else consistently is magic unicorn machine type stuff.If your bomb looks like thismaybe it will be found on an X-ray. However no-one is so stupid as to make their bomb look like that so good luck. The reality is that a terrorist is going to make a bomb look like this.Note they have to have labels to describe what things are and actually a terrorist is going to make it look a whole lot less detectable than than. We know that this type of thing can make it through the pointless airport security.Ultimately your chance of being killed by a terrorist on an airplane is much lower than your chance of drowning in your own bathtub or dying from an asteroid collision with earth. By the way the risks are not even close - drowning in your bathtub and asteroids are much more dangerous!!!!Some Further Country Specific Type Stuff=======================================USA TSA-Pre and associated trusted traveler programs============================================You can sign up for these and there are many programs that do basically the same thing (check to see which one is cheapest), but signing up is a complete PIA. You have to go for a screening interview and have a background check. When I went for my screening interview half the people there had been scheduled to go for their interview at 2am and were a little bit confused when they didn’t realize their 0200 interview time did mean 2 in the afternoon. Its bureaucratic and unbelievably pointless - seriously what do you think the bored agent is going to do in an interview with me - use his psychic powers to read my mind to figure out that I am a terrorist! This program will keep former juvenile shoplifters off airplanes but little else.London======Some places whether they say it or not practice profiling. If I travel through London they have the annoying habit of pretending that the metal detector has gone off whenever a single male (that's me) is travelling through there. When I point out that I didn't have any metal on me and I know that I could not have set the metal detector off - they have the temerity to claim that I was "randomly selected" even though the statistical chance of me being "randomly" selected every time are vanishingly small.Israel======Israel is famous for their profiling (as well as the professionalism of their security staff). For some reason your level of suspicion is higher if you arrive right before your flight (as if a terrorist who’s spent a year planning is going to be running late) so try to arrive in plenty of time. Other than that they ask lots of questions. You are typically talking to a rather intense Israeli security person who you've never met before and wants to know everything about why you are going to Israel in a completely artificial discussion. The most natural thing in the world is to give short one word answers and look a little uncomfortable. But that’s absolutely the worst thing you can do (they are looking for nervous and shifty people remember) so my usual strategy there is to just keep talking and talking and talking and talking - show them you have nothing to hide - give them every detail before they have a chance to ask for it (and they will ask) - make it clear that you are completely relaxed talking to them about everything and do your best to talk so much they can’t get a word in edgewise - if they do somehow manage to penetrate your wall of verbal diarrhea they will only ask you questions that might make you feel uncomfortable and look shifty. If you follow this strategy they will soon say: “Enough!” and you’ll be on your way.Other than that happy travels - and don’t forget to write to your political leaders to tell them how pointless this all is and ask them if they couldn’t better spend the billions wasted on airport security on roads, schools and libraries.

The practical method is as follows:1) As you walk up to the line observe which ones are using a magnetometer (metal detector) if at all possible get in to that line.2) If you can, ask security if we are removing shoes today (this varies from country to country and sometimes month to month - security pretends to follow a consistent protocol but that just ain't so).3) While waiting in line remove any metal objects (e.g. keys, wallet of coins, beltbuckles) and place them in your jacket or whatever bag you are carrying - anything you aren't going to take through the magnetometer. I usually do not remove my wedding ring but more on that later.4) With one action pick up 4 trays, and drop them from the bottom of your stack one by one like you are laying plates. Leave space between the first 2 and the last two (this is for your roll aboard).5) Place your items on the belt in the following order-Shoes (if you need to take them off)-Jacket-Roll aboard-Computer bag-Computer5) Wait to be asked through the magnetometer (remember I said always pick the line with the metal detector if you can - not the slow and quite frankly useless nude body scanners). When asked walk through as close to the center as possible, keep hands in the center of the body - if you wear a ring the center of the magnetometer is the least sensitive place and is unlikely to cause an alarm.6) When you get to the other side your items should come out in optimal order. Put your shoes and jacket on first.7) Place your roller aboard on the ground and your computer bag on top of this.8) The computer takes longest to screen so you should have had plenty of time to get organised and all you need to do is place the computer in your computer bag that is sitting on the roll aboard and can walk off.9) Write to your congressman. We’d get a lot more speed if everyone who read this answer would, right now, write a three sentence email to their congressman saying:"Please get rid of the pointless and wasteful TSA. As a brave American I don't need a false sense of security and I'd like you to spend the money instead on schools, roads, and libraries. Passengers have proven they will take care of themselves much better than the guys with rubber gloves ever will, thank you very much."At a minimum we'd get some movement in the right direction and writing to congress en mass does work. To find your representative look at:https://www.house.gov/representatives/find-your-representativeA little bit more detail for those who want to write at length:https://www.thoughtco.com/write-effective-letters-to-congress-3322301Couple of Notes==============Note I didn't say remove liquids and gels. Now, I would never advocate deliberately attempting to evade detection or deliberately leaving this stuff in there - you should dump it before getting to the airport. But the reality is that I've forgotten that stuff in with my computer cables so many times I know that they basically rarely ever find it. Once I was drinking a half gallon sized bottle of milk on my way to the airport, got busy and distracted when I got there forgot about it in my computer bag and it sailed through. Once I left a quart sized bottle of shampoo in there by mistake again my bag has sailed through. So don't waste your time searching your bag for it.I spent my PhD and post-doc designing scanners that while not identical to airport security systems are closely related. So, try not to snigger too much when the TSA uses a "magic" machine that purportedly detects explosives, dangerous liquids or unicorns. I’ll leave you to search the internet for stories from people who after tours in Iraq had visible explosive residue on the exterior of their bags that didn’t set of any alarms from the “magic” machine. If you think that such "magic" machines actually work on a consistent basis I have an investment opportunity in Nigeria for you.Remember the TSA's own tests show that 95% of the time they can not find contraband (see TSA's 95% failure rate shows airport security is a charade - Los Angeles Times). Don't waste your time searching your bag for it - the TSA probably will not find it. The above instructions are optimized for what the airport security can find. For example they can easily figure out if you are wearing shoes and so might ask you to take them off - the fact that they can't tell if the shoes are made of C4 or swiss cheese is obviously irrelevant to them. They can figure out if you are wearing a jacket so might ask you to take it off, however they will never figure out if that jacket is made of gun-cotton. They can easily find a metal object bigger than a wedding ring on your person. Trying to detect pretty much anything else consistently is magic unicorn machine type stuff.If your bomb looks like thismaybe it will be found on an X-ray. However no-one is so stupid as to make their bomb look like that so good luck. The reality is that a terrorist is going to make a bomb look like this.Note the need for labels so that you can see its actually a bomb.Actually no - they are going to make it look a whole lot less detectable than than. We know that this type of thing can make it through the pointless airport security. Ultimately it will look like something that passes through airport security all the time.Ultimately your chance of being killed by a terrorist on an airplane is much lower than your chance of drowning in your own bathtub or dying from an asteroid collision with earth. By the way the risks are not even close - drowning in your bathtub and asteroids are much more dangerous!!!!Some Further Country Specific Type Stuff=======================================USA TSA-Pre and associated programs================================You can sign up for these and there are many programs that do basically the same thing (check to see which one is cheapest), but signing up is a complete PIA. You have to go for a screening interview and have a background check. When I went for my screening interview half the people there had been scheduled to go for their interview at 2am and were a little bit confused when they didn’t realize their 0200 interview time did mean 2 in the afternoon. Its bureaucratic and unbelievably pointless - seriously what do you think the bored agent is going to get out of an interview with me? What is he going to ask to see if I am a threat? Do you seriously think that a terrorist recruiter is going to find someone with a US criminal record and put them on a terrorist mission. If I had a history of cleptomania I am sure I would have been denied - its not clear that a potential terrorist would.London======Some places whether they say it or not practice profiling. If I travel through London they have the annoying habit of pretending that the metal detector has gone off whenever a single male (that's me) is travelling through there. When I point out that I didn't have any metal on me and I know that I could not have set the metal detector off - they have the temerity to claim that I was "randomly selected" even though the statistical chance of me being "randomly" selected every time are vanishingly small.Israel======Israel is famous for their profiling (as well as the professionalism of their security staff). For some reason your level of suspicion is higher if you arrive right before your flight (as if a terrorist who’s spent a year planning is going to be running late) so try to arrive in plenty of time. Other than that they ask lots of questions - so my usual strategy there is to just keep talking and talking and talking and talking - show them you have nothing to hide - give them every detail before they have a chance to ask for it (and they will ask) - make it clear that you are completely relaxed talking to a rather intense Israeli security person who you've never met before and wants to know everything about why you are going to Israel in a completely artificial discussion.Other than that happy travels - and don’t forget to write to your political leaders to tell them how pointless this all is and ask them if they couldn’t better spend the billions wasted on airport security on roads, schools and libraries.

From the docs themselves:Use the Production BuildIf you’re benchmarking or experiencing performance problems in your React apps, make sure you’re testing with the minified production build.By default, React includes many helpful warnings. These warnings are very useful in development. However, they make React larger and slower so you should make sure to use the production version when you deploy the app.If you aren’t sure whether your build process is set up correctly, you can check it by installing React Developer Tools for Chrome. If you visit a site with React in production mode, the icon will have a dark background:If you visit a site with React in development mode, the icon will have a red background:It is expected that you use the development mode when working on your app, and the production mode when deploying your app to the users.You can find instructions for building your app for production below.Create React AppIf your project is built with Create React App, run:npm run build This will create a production build of your app in the build/ folder of your project.Remember that this is only necessary before deploying to production. For normal development, use npm start.Single-File BuildsWe offer production-ready versions of React and React DOM as single files:<script src="https://unpkg.com/react@16/umd/react.production.min.js"></script> <script src="https://unpkg.com/react-dom@16/umd/react-dom.production.min.js"></script> Remember that only React files ending with .production.min.js are suitable for production.BrunchFor the most efficient Brunch production build, install the terser-brunch plugin:# If you use npm npm install --save-dev terser-brunch  # If you use Yarn yarn add --dev terser-brunch Then, to create a production build, add the -p flag to the build command:brunch build -p Remember that you only need to do this for production builds. You shouldn’t pass the -p flag or apply this plugin in development, because it will hide useful React warnings and make the builds much slower.BrowserifyFor the most efficient Browserify production build, install a few plugins:# If you use npm npm install --save-dev envify terser uglifyify   # If you use Yarn yarn add --dev envify terser uglifyify  To create a production build, make sure that you add these transforms (the order matters):The envify transform ensures the right build environment is set. Make it global (-g).The uglifyify transform removes development imports. Make it global too (-g).Finally, the resulting bundle is piped to terser for mangling (read why).For example:browserify ./index.js \  -g [ envify --NODE_ENV production ] \  -g uglifyify \  | terser --compress --mangle > ./bundle.js Remember that you only need to do this for production builds. You shouldn’t apply these plugins in development because they will hide useful React warnings, and make the builds much slower.RollupFor the most efficient Rollup production build, install a few plugins:# If you use npm npm install --save-dev rollup-plugin-commonjs rollup-plugin-replace rollup-plugin-terser  # If you use Yarn yarn add --dev rollup-plugin-commonjs rollup-plugin-replace rollup-plugin-terser To create a production build, make sure that you add these plugins (the order matters):The replace plugin ensures the right build environment is set.The commonjs plugin provides support for CommonJS in Rollup.The terser plugin compresses and mangles the final bundle.plugins: [  // ...  require('rollup-plugin-replace')({  'process.env.NODE_ENV': JSON.stringify('production')  }),  require('rollup-plugin-commonjs')(),  require('rollup-plugin-terser')(),  // ... ] For a complete setup example see this gist.Remember that you only need to do this for production builds. You shouldn’t apply the terser plugin or the replace plugin with 'production' value in development because they will hide useful React warnings, and make the builds much slower.webpackNote:If you’re using Create React App, please follow the instructions above.This section is only relevant if you configure webpack directly.Webpack v4+ will minify your code by default in production mode.const TerserPlugin = require('terser-webpack-plugin');  module.exports = {  mode: 'production'  optimization: {  minimizer: [new TerserPlugin({ /* additional options here */ })],  }, }; You can learn more about this in webpack documentation.Remember that you only need to do this for production builds. You shouldn’t apply TerserPlugin in development because it will hide useful React warnings, and make the builds much slower.Profiling Components with the Chrome Performance TabIn the development mode, you can visualize how components mount, update, and unmount, using the performance tools in supported browsers. For example:To do this in Chrome:Temporarily disable all Chrome extensions, especially React DevTools. They can significantly skew the results!Make sure you’re running the application in the development mode.Open the Chrome DevTools Performance tab and press Record.Perform the actions you want to profile. Don’t record more than 20 seconds or Chrome might hang.Stop recording.React events will be grouped under the User Timing label.For a more detailed walkthrough, check out this article by Ben Schwarz.Note that the numbers are relative so components will render faster in production. Still, this should help you realize when unrelated UI gets updated by mistake, and how deep and how often your UI updates occur.Currently Chrome, Edge, and IE are the only browsers supporting this feature, but we use the standard User Timing API so we expect more browsers to add support for it.Profiling Components with the DevTools Profilerreact-dom 16.5+ and react-native 0.57+ provide enhanced profiling capabilities in DEV mode with the React DevTools Profiler. An overview of the Profiler can be found in the blog post “Introducing the React Profiler”. A video walkthrough of the profiler is also available on YouTube.If you haven’t yet installed the React DevTools, you can find them here:Chrome Browser ExtensionFirefox Browser ExtensionStandalone Node PackageNoteA production profiling bundle of react-dom is also available as react-dom/profiling. Read more about how to use this bundle at fb.me/react-profilingVirtualize Long ListsIf your application renders long lists of data (hundreds or thousands of rows), we recommended using a technique known as “windowing”. This technique only renders a small subset of your rows at any given time, and can dramatically reduce the time it takes to re-render the components as well as the number of DOM nodes created.react-window and react-virtualized are popular windowing libraries. They provide several reusable components for displaying lists, grids, and tabular data. You can also create your own windowing component, like Twitter did, if you want something more tailored to your application’s specific use case.Avoid ReconciliationReact builds and maintains an internal representation of the rendered UI. It includes the React elements you return from your components. This representation lets React avoid creating DOM nodes and accessing existing ones beyond necessity, as that can be slower than operations on JavaScript objects. Sometimes it is referred to as a “virtual DOM”, but it works the same way on React Native.When a component’s props or state change, React decides whether an actual DOM update is necessary by comparing the newly returned element with the previously rendered one. When they are not equal, React will update the DOM.Even though React only updates the changed DOM nodes, re-rendering still takes some time. In many cases it’s not a problem, but if the slowdown is noticeable, you can speed all of this up by overriding the lifecycle function shouldComponentUpdate, which is triggered before the re-rendering process starts. The default implementation of this function returns true, leaving React to perform the update:shouldComponentUpdate(nextProps, nextState) {  return true; } If you know that in some situations your component doesn’t need to update, you can return false from shouldComponentUpdate instead, to skip the whole rendering process, including calling render() on this component and below.In most cases, instead of writing shouldComponentUpdate() by hand, you can inherit from React.PureComponent. It is equivalent to implementing shouldComponentUpdate() with a shallow comparison of current and previous props and state.shouldComponentUpdate In ActionHere’s a subtree of components. For each one, SCU indicates what shouldComponentUpdate returned, and vDOMEq indicates whether the rendered React elements were equivalent. Finally, the circle’s color indicates whether the component had to be reconciled or not.Since shouldComponentUpdate returned false for the subtree rooted at C2, React did not attempt to render C2, and thus didn’t even have to invoke shouldComponentUpdate on C4 and C5.For C1 and C3, shouldComponentUpdate returned true, so React had to go down to the leaves and check them. For C6 shouldComponentUpdate returned true, and since the rendered elements weren’t equivalent React had to update the DOM.The last interesting case is C8. React had to render this component, but since the React elements it returned were equal to the previously rendered ones, it didn’t have to update the DOM.Note that React only had to do DOM mutations for C6, which was inevitable. For C8, it bailed out by comparing the rendered React elements, and for C2’s subtree and C7, it didn’t even have to compare the elements as we bailed out on shouldComponentUpdate, and renderwas not called.ExamplesIf the only way your component ever changes is when the props.color or the state.count variable changes, you could have shouldComponentUpdate check that:class CounterButton extends React.Component {  constructor(props) {  super(props);  this.state = {count: 1};  }   shouldComponentUpdate(nextProps, nextState) {  if (this.props.color !== nextProps.color) {  return true;  }  if (this.state.count !== nextState.count) {  return true;  }  return false;  }   render() {  return (  <button  color={this.props.color}  onClick={() => this.setState(state => ({count: state.count + 1}))}>  Count: {this.state.count}  </button>  );  } } In this code, shouldComponentUpdate is just checking if there is any change in props.color or state.count. If those values don’t change, the component doesn’t update. If your component got more complex, you could use a similar pattern of doing a “shallow comparison” between all the fields of props and state to determine if the component should update. This pattern is common enough that React provides a helper to use this logic - just inherit from React.PureComponent. So this code is a simpler way to achieve the same thing:class CounterButton extends React.PureComponent {  constructor(props) {  super(props);  this.state = {count: 1};  }   render() {  return (  <button  color={this.props.color}  onClick={() => this.setState(state => ({count: state.count + 1}))}>  Count: {this.state.count}  </button>  );  } } Most of the time, you can use React.PureComponent instead of writing your own shouldComponentUpdate. It only does a shallow comparison, so you can’t use it if the props or state may have been mutated in a way that a shallow comparison would miss.This can be a problem with more complex data structures. For example, let’s say you want a ListOfWords component to render a comma-separated list of words, with a parent WordAdder component that lets you click a button to add a word to the list. This code does not work correctly:class ListOfWords extends React.PureComponent {  render() {  return <div>{this.props.words.join(',')}</div>;  } }  class WordAdder extends React.Component {  constructor(props) {  super(props);  this.state = {  words: ['marklar']  };  this.handleClick = this.handleClick.bind(this);  }   handleClick() {  // This section is bad style and causes a bug  const words = this.state.words;  words.push('marklar');  this.setState({words: words});  }   render() {  return (  <div>  <button onClick={this.handleClick} />  <ListOfWords words={this.state.words} />  </div>  );  } } The problem is that PureComponent will do a simple comparison between the old and new values of this.props.words. Since this code mutates the words array in the handleClick method of WordAdder, the old and new values of this.props.words will compare as equal, even though the actual words in the array have changed. The ListOfWords will thus not update even though it has new words that should be rendered.The Power Of Not Mutating DataThe simplest way to avoid this problem is to avoid mutating values that you are using as props or state. For example, the handleClick method above could be rewritten using concat as:handleClick() {  this.setState(state => ({  words: state.words.concat(['marklar'])  })); } ES6 supports a spread syntax for arrays which can make this easier. If you’re using Create React App, this syntax is available by default.handleClick() {  this.setState(state => ({  words: [...state.words, 'marklar'],  })); }; You can also rewrite code that mutates objects to avoid mutation, in a similar way. For example, let’s say we have an object named colormap and we want to write a function that changes colormap.right to be 'blue'. We could write:function updateColorMap(colormap) {  colormap.right = 'blue'; } To write this without mutating the original object, we can use Object.assign method:function updateColorMap(colormap) {  return Object.assign({}, colormap, {right: 'blue'}); } updateColorMap now returns a new object, rather than mutating the old one. Object.assign is in ES6 and requires a polyfill.There is a JavaScript proposal to add object spread properties to make it easier to update objects without mutation as well:function updateColorMap(colormap) {  return {...colormap, right: 'blue'}; } If you’re using Create React App, both Object.assign and the object spread syntax are available by default.When you deal with deeply nested objects, updating them in an immutable way can feel convoluted. If you run into this problem, check out Immer or immutability-helper. These libraries let you write highly readable code without losing the benefits of immutability.