The Art of Forgetting

I had a mini-technical interview last week for a backend developer role using Ruby as the main language. While the questions were not very tough, it’s been a while since I had to explain technical concepts – especially under pressure.

Unfortunately, we don’t get too many do-overs in life, but we can learn from the past and keep moving forward. When we face the same problem in the future, we can hopefully handle it better. What can we do to help our future selves? One thing we can do is write about things we have learned. This will hopefully plant them more firmly in our minds. I thought I’d write out the questions and answer them how I would have liked to have answered them if I could answer them again. Whew. Without further ado, let’s jump in.

First question – Which http status codes exist and what do they mean?

I admit, it was a pretty easy one – just a general, low-level question. I had an ok answer, but I’ll give it another go. Http status codes range from 100 to 500. The most common codes being in the 200, 400, and 500 ranges. A 200 means the request went through successfully – not much more to it than that. Anything in the 400’s means that the connection to the server was ok but request was not good from the client. This could be anything ranging from an incomplete form to one of the most common – a 404 – which means the path was not found. Basically, if we type in an address such as http://www.weather.com/alskdjf, the request will hit the server and the path (alskdjf) will try to be found. In this case it won’t and the request will come back as a 404. Most developers will take this into consideration when building a website/web app and route you to their 404 page.

Screen Shot 2018-10-19 at 4.53.57 PM

weather.com’s 404 page

An http status code in the 500’s means that there was an Internal Server Error. It could be that the server is down at the moment, or quite possibly it just doesn’t like you:)

Second question – What http methods are there?

It should have been another layup. Again, my answer was ok, but I’ll try again. There are quite a few http methods, but the most common ones used for RESTful architecture are GET, POST, PUT, PATCH and DELETE.

Follow up – What is the difference between POST, PUT, and PATCH?

A POST request will create a new resource at the provided URI. So let’s say we are creating a new account on Facebook. When we fill out our information and hit submit, a POST request will be sent to create a new resource in the database with our info. A PUT request will either find the existing resource and replace the whole resource with the new one. Or if the resource doesn’t already exist, a new one will be created. A PATCH request will update an existing resource. Say we want to update our email address on our FB profile. When the PATCH request goes through, it will find our existing information and update just the email portion of the resource – not the whole resource.

Third question – What does indexing do?

Welp, I’ve actually been using indexes quite often with MarkLogic (eek!), but my mind turned turned off at this point. I think I said something about primary keys in a table and associations between tables. As soon as I stopped talking I knew I was way off. Let’s try that again.

Indexing is used to speed up data retrieval from the database. Think of a book. Now imagine we wanted to find the page that a certain topic was on. What would we do? We would go to the index and find what page it was on! Now imagine this book didn’t have an index. We would be forced to scan every page in the book to try and find what we were looking for. This is very similar to what would happen if we didn’t have an index on our table.

Indexing is configured by putting a data structure on a column in a table. This data structure, in most cases a B-tree, acts as a pointer to data in a table. For example, we visit FB and we want to look up an acquaintance in the search bar by their last name. Let’s say our acquaintance’s last name is “Yorke”. If the “last_name” column is not indexed in the table, the query will have to run through every single row in the table to find the users with the last name of Yorke. With billions of users stored in the table, that could take some time. However, if the “last_name” column is indexed, the query will run significantly faster.

Fourth question – Explain composition over inheritance

I knew I read about these concepts last year when I was studying a few design patterns, but in the heat of the moment, I just couldn’t recall. I think I mumbled something about classical inheritance being bad…something, something, something. It’s amazing what a little refresher will do!

Both composition and inheritance are design patterns in Object Oriented programming that we can use to keep our code DRY. In other words, they let us reuse code but in very different ways.

Inheritance

With inheritance, types are defined by what they are. So let’s say we have a monkey. Well, a monkey is an animal, so monkeys can inherit characteristics that all animals share. That sounds pretty reasonable to me, so what’s the issue?

One of the arguments against inheritance is that things might change down the line. We are forced to predict future behavior of our classes without having all of the information we may need. The example above is a very simple one, but in the real world, we would most likely have an inheritance tree. Imagine the whole animal kingdom mapped out this way using inheritance. If we had to make any changes in the base class, it would likely have consequences for all the subclasses and quite possibly break much of our code. This makes inheritance very inflexible as a design pattern because we can’t make changes without breaking a lot of our code.

So should we avoid inheritance like the plague? Nope, not at all! Like any tool, we just have to use it wisely. We wouldn’t use a hammer if all we had were screws. The rule of thumb here is to use inheritance if you have a shallow tree and you know for sure that your parent class isn’t going to change. If we shouldn’t use inheritance, what should we use?

Composition

We learned earlier that when we use inheritance, our types are defined by what they are. When we use composition, our types are defined by what they do. Here we don’t have to predict the future behavior of our classes, which will leave us with many less headaches down the line. We can pick and choose what are objects look like based on what they do. Maybe all we need our monkey to do is see, swing from a tree and eat a banana. Our Monkey class will only be given these methods – and only these methods. Now our monkeys are lean and not weighed down with a ton of baggage they ultimately won’t use.

Forget Me Not

To my future self – You’re welcome.

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Rails, AngularJS (1.5.8), and Webpack — Part 3

Alrighty then. Where were we? I believe we left off in a good place. We installed the webpacker gem, and seemed to have communication between our newly created JS file and our app. Now for the hard part. I’m still learning this stuff myself, so bear with me. We’re going to attempt to use ES6 modules instead of the old way of declaring AngularJS components and such. This style guide is a good starting point to get to know what your components will look like and how they’ll interact with each other.

Setting up the Main Module

The first thing we’ll want to do is setup up our main Angular module in app/javascript/packs/application.js. First we have to import angular into the file so our module knows what it’s attaching itself to. We are also going to export the module, which will allow our webpack to compile it when we run app in the terminal.

// app/javascript/packs/application.js

import angular from 'angular';

const meals = angular.module('meals', [])

export default meals;

Now we have to declare our app in our main html file: app/views/layouts/application.html.erb. So in the body tag, add ng-app=”meals”.

<!DOCTYPE html>
<html>
  <head>
    <title>Meals</title>
    <%= csrf_meta_tags %>

    <%= stylesheet_link_tag    'application', media: 'all' %>
    <%= javascript_include_tag 'application' %>
    <%= javascript_pack_tag 'application' %>
  </head>

  <body ng-app="meals">
    <%= yield %>
  </body>
</html>

Now our app knows that it’s an Angular app and it’s looking for a module called ‘meals’. Let’s add a route with a component so we can actually see something working on the Angular side of the world.

Routing With angular-ui-router

If you’ve built anything with Angular in the past, you’ve most definitely used angular-ui-router. We’re going to install it with yarn. If you don’t have yarn installed, check out the installation instructions here. To install, or ‘add’ as it’s called in yarnish, head over to your terminal and type: ‘yarn add angular-ui-router’. If you check your dependencies in your package.json file, you should see ‘angular-ui-router’ listed.

So let’s see if we can get a route working. In our angular_home.html file, let’s add a ui-view directive.

<-- app/views/application/angular_home.html -->

<ui-view></ui-view>

This will give us an entry point into AngularLand and let us declare routes with $stateProvider in a config function. Back in our application.js file, let’s add a config function and a route. First we’ll have to import the ui-router so we can use all of its goodness. Check it…

// app/javascript/packs/application.js

import angular from 'angular';
import uirouter from 'angular-ui-router';

const meals = angular.module('meals', [uirouter])
  .config(($stateProvider) => {
    $stateProvider
      .state('home', {
        url: '/',
        template: `<h1>Hola Mundo!</h1>`
      })
  })

export default meals;

Ok so here we’re importing the angular-ui-router and chaining a config function onto our module. Angular-ui-router gives us access to $stateProvider, $urlRouterProvider, $state, and $stateParams. In the config function above, we’re using the Arrow function syntax now available in ES6, and setting the state. With a url and a simple template, we should be getting somewhere. Let’s quickly make a link back in angular_home.html so we can see our route is working.

<-- app/views/application/angular_home.html -->

<a ui-sref="home">Home</a>
<ui-view></ui-view>

Run the Webpack and Rails Server Simultaneously?

Now to run webpack, we can’t just run the rails server. We actually have to run the rails and the webpack servers. Back in the terminal, create a new tab in the same directory, then run ‘./bin/webpack-dev-server’. This will compile your included javascript files through webpack. If you’re like me, then you probably got a lot of red errors followed by this line: webpack: Failed to compile.

So something is not letting us load our module. If we scroll up in the terminal, we’ll see that most of the errors say that angular doesn’t exist. But I thought we installed Angular already!! Well, I’m pretty sure that when we installed it with the webpacker command, it installed Angular 4. We need version 1.5.8, which we can easily install add with yarn. Exit out of the webpack server in your terminal. Then type ‘yarn add angular@1.5.8’.

Check out your package.json file and you should see angular with the correct version listed under the dependencies. Now if we try to run the server again – ‘./bin/webpack-dev-server’ – everything should compile (there might be a few warnings, but let’s not worry about those). In your other tab run the rails server command and in your browser go to ‘localhost:3000’. You should see a link that says ‘Home’. Click it, and you should be routed to the home route that we set up earlier. If you followed along, you should see ‘Hola Mundo!’ on the webpage!

To Sum it Up

We are in the Angular business now! In this episode, we’ve connected the front end to our meals app with webpack, added angular-ui-router and AngularJS, created our main module with a route and template, learned how to run the webpack server, and saw our template working in the browser. Next time, we’ll get some functionality going with some http requests to the backend and do something a little more exciting than Hello World Hola Mundo. As always, thanks for reading. I hope this helps someone out there! Until next time…CHEERS:)

Removing whitespace from a string in Ruby vs. JavaScript

I’m back from vacation. After visiting my family in Long Island, we ventured up to the Catskills for a few nights, which culminated with my younger sister getting married. It was a very cool wedding! The next day, my wife, nephew, and I drove up to Montreal to see her folks. Montreal is one of my favorite cities (in the summer) – it has very European feel. As great as it is to get away, it’s always hard to get back into the groove after a trip. I’m just getting my sea legs back under me so this post is going to be short and sweet.

Have you ever needed to get rid of leading and trailing whitespace from a string? It’s a good rule of thumb to do just that to any input you’re receiving on a form. Luckily, it’s quite easy in most languages. Let’s take a look at how we’ll approach this in Ruby first.

str = "  How's it going?   "
=> "  How's it going?   "
# Let's get rid of that whitespace
str.strip()  
=> "How's it going?"
str 
=> "  How's it going?   "
# We didn't permanently change the string itself
# Most methods are non-destructive, but Ruby let's us be destructive if we 
# really want to. We just got to bang it (pun intended)
str.strip!() 
"How's it going?"
str 
=> "How's it going?"

Pretty simple! Let’s take a look at how to do this in JavaScript.

let str = "  How's it going?   ";
str.trim(); 
'How/'s it going?'
str  
'   How\'s it going?   '
// There's no permanent destructive way to change strings in JavaScript - they 
// are immutable. So we just have to reassign our variable like so...
str = str.trim();
'How\'s it going?'
str  
'How\'s it going?'

I mentioned that strings in JavaScript are immutable. This means the string cannot be changed in memory. So when we call a method like trim or slice on a string, the return value is a new string. Like the example above, we have to reassign ‘str’ to the return value of the method call. In Ruby however, strings are mutable. Let’s take a look.

str = "  Trim me  "
str.object_id 
=> 70365544319940 
str.strip!()
=> "Trim me"
str.object_id
=> 70365544319940 
# Even though we changed the string, the id is still the same
# We can also change characters in place, which cannot be done in JS
str[7] = '!'
=> '!'
str
=> "Trim me!"
# Pretty cool!
str.object_id
=> 70365544319940 
# No change

That’s it for this week. Always remember how cool Ruby can be. It makes life easier in many ways. JavaScript however, can do much more. It is not only an Object Oriented language, but a multi-paradigm language! From Wikipedia:

As a multi-paradigm language, JavaScript supports event-driven, functional, and imperative (including object-oriented and prototype-based) programming styles. It has an API for working with text, arrays, dates, regular expressions, and basic manipulation of the DOM, but does not include any I/O, such as networking, storage, or graphics facilities, relying for these upon the host environment in which it is embedded.

Thanks Wikipedia! Until next time! Cheers:)

How to Clone a Website Using Chrome’s Dev Tools Part I

Ever want to copy a website? Well, it’s pretty easy – especially with Chrome’s Dev Tools! I find it pretty useful to go into someone else’s code to see how they’re doing what they’re doing. Then you can implement new cool features for sites you’re working on. I’m not going into complicated websites with API’s and the like; just a simple static site.

I’m going to be using Carbon Five’s website as reference. First head on over there, then right click on the page and select ‘view page source’. This will show us all the html for the page. Now just select all (command + ‘a’) and copy. In your text editor of choice (I’m using Atom), create an index.html file and paste the html there. You’ll see a bunch of files that are referenced in the ‘head’ of the document. We’ll have to copy the non-CDN local files into our text editor.

We’re going to open each file from the page source and copy file into our text editor.

Screen Shot 2017-07-02 at 3.41.31 PM

Create folders for each type of file, ie. javascripts, stylesheets, images, etc. We’re going to do what we did above when copying and pasting all of the HTML. Starting from the ‘javascripts/showup.js’ file in the head of the view source page document, click on each file, select all, copy (noticing a trend?) and paste into a newly created file in Atom. Name the file the same as the file you’re copying from. From here, let’s see where we stand by opening the index.html file in Chrome. Go ahead, I’ll wait…

Screen Shot 2017-07-02 at 5.24.47 PM

It should look something like this

Woah! All of a sudden we’re in 1995 and Nirvana’s on the radio! We’re getting the bare bones HTML here. Let’s take a look in the console to see what’s going on under the hood. Command + option + ‘j’ will get us there. Notice all of the errors.

Screen Shot 2017-07-02 at 5.30.38 PM

That’s a lotta red

There are a ton of files that can’t be found. There are definitely some files we haven’t looked at yet, but let’s focus on the ones we have. Our file directory must be different than Carbon Five’s. All we have to do is reference them a bit differently than we are.

Let’s look at the non-CDN files in the ‘head’ of our index.html page. They all start with a forward slash, but if we’re referencing from the index.html file, we’ll have to prepend them with a single period to jump up to the root directory. Start from the ‘showup.js’ file start adding.

<script type="text/javascript" src="/javascripts/showup.js"></script> // This
// Turns into 
<script type="text/javascript" src="./javascripts/showup.js"></script>

When you’re done (remember to save), refresh your index.html file in Chrome. You’ll notice a few things happened. The page has some styling now – not great, but it’s something. Next, we have less errors in the console. Sweet! Let’s keep going and turn these errors green.

In the console, notice how the cdn files which can’t be found start with two forward slashes. Since they are referencing outside websites as opposed to local files, we’ll have to prepend them with ‘https:’, and they should be good to go. Back in our index.html file, let’s do just that. Once you’re done, notice how the links turn blue. We now have good links. Go back to your browser and refresh.

Screen Shot 2017-07-02 at 5.41.40 PM

Getting there!

Now we’re talking! Since we’re now referencing the bootstrap cdn files correctly, we have our navbar looking good and the page layout is looking much better. Next time, we’ll add images and conquer any other errors we come across. Until then, CHEERS:)

I’ve Got 99 Problems – but Deploying My Rails/Angular App to Heroku is No Longer One of Them:) PART 2

So where was I? Oh yeah, I left off at changing my problem js file extensions to ‘.es6’ so there would be no problem with new JS6 syntax. This definitely helped, but in it’s place sprung another problem. Only the images that were not hooked up to the database on my site were showing . So I used my noggin and realized that I never migrated my database to Heroku! DOH!

When I tried to run ‘heroku run rake db:migrate’, the migration kept aborting with this message:

PG::UndefinedTable: ERROR:  relation "users" does not exist

I definitely had a table called “users” so that didn’t make much sense. I did a little digging and found out that postgres (the database Heroku uses) does not like tables relating to other tables that have not been created yet. The table being created was referencing a table that was created on a later migration. I know it’s not a good idea to mess with the names of migration files, but I did anyway. Rails timestamps migration files, so I just had to change my “users” file timestamp to a date before the file in question.

So I tried the migrate command again and got the same error. Strange. My migration files had quite a few additions which later became subtractions. I decided that I only really needed three migrations for three tables. Since I had a good seed file which could recreate everything I needed, I decided to recreate only the migrations I needed. This would allow me to reset the database and start from scratch. I deleted the schema and development.sqlite3 files so there would be no references to the old migrations. Now I could recreate my database and schema file.

$ rails db:drop db:create db:migrate db:seed
// This will delete the entire database, losing all data
// recreate a new database and runs the migrations
// db:seed will seed the database from seeds.rb

I had a brand spanking new schema and database, ran my local server and everything was running smoothly. So I ran the heroku migration command again and got THE SAME ERROR!! WTF?!? After googling for a bit, it hit me. I didn’t push the new changes to heroku! Often times it is the simple tasks that one might forget to do that causes errors. Note to self: if you are banging your head against the wall, stop for a minute and think of the steps you would normally take. Save yourself some time and energy. The first change to the “users” migration file name probably would have worked if I just slowed down a little.

After trying to migrate to Heroku again, it worked! Now my site is up and running, and I’m feeling good! Hopefully this helps fellow programmers out there that get stuck – and have sore heads! As always, thanks for reading!

Adding a Gradient to a Background Image with CSS

I’ve been building a portfolio site for myself and came across a small problem. I wanted the navbar to be transparent on the hero part of the page, however, the text in the navbar wasn’t showing up very well with the background image that I was using. Take a look…

Portfolio-site screengrab

Background image without gradient at top

Notice the navbar text. Not very clear if you ask me. What to do? If I had a bit of gradient at the top, that would let the text pop more. Of course I could use Photoshop to transform the image, but being a developer, I wanted to do it with code. It turned out I could accomplish what I wanted with CSS. I have to admit, even though I’m a Full Stack Developer, CSS has never been my thing. But I have to say it’s been growing on me lately. The CSS for my background image looked like this:

.background {
  background-repeat:no-repeat;
  background-position:50% 50%;
  background-image: url('../images/road-trees.jpg');
}

Pretty simple. The color of gradient at the top of the image should be within the image that I was working with. I found a cool extension for Chrome called ColorPick Eye Dropper that gives you a color picker that you can use for whatever website you’re on. I used this to find a nice dark green in my image. The CSS is quite simple. You just have to add a linear gradient to the background image styling like so.

.background {
  background-repeat:no-repeat;
  background-position:50% 50%;
  background-image: linear-gradient(
      rgba(18, 39, 32, 0.9),
      rgba(255, 255, 255, 0)
    ),url('../images/road-trees.jpg');
}

The first value of the linear-gradient represents the top of the image and the second, you guessed it, is the bottom. The last value of the rgba is the opacity. As you can see, the second value is white with an opacity of 0, which makes it transparent. This gives us the final product.

TJ portfolio hero

Image with CSS gradient at top

I’m not a designer, but I know that looks better. Everything is popping nicely. Happy coding:)

The Big O

First off, this is a technical blog. My apologies if you came here looking for something a little sexier. Not that Big O Notation can’t be sexy. Depends on what floats your boat or sinks your battleship. Anywho, the following is a little teaser on Big O.

Foreplay

When you take your first few steps learning how to program, something like Big O Notation is the furthest thing from your mind. Learning to code is hard. Period. There is so much to know, and quite frankly, it is daunting. Imagine looking up at the highest peaks of Mt. Everest from the bottom of the mountain. Now imagine that the mountain is always shifting and getting bigger. That’s what it feels like when you start learning. Somewhere along the way (hopefully), your footing will become more secure on the shifting ground and you’ll gain some comfortability in the place of not knowing. Because nobody knows it all. Keep one foot in front of the other and keep climbing. Try to enjoy the ride.

If you went to a bootcamp, there was so much knowledge being pushed into your brain in a few short months. Bootcamps are great, but they just focus on web development. When you graduate and start to prepare for interviews, you begin to hear scary terms that you never heard before. Things like Linked Lists, Big O Notation, Bitwise Operators, Binary Trees, Stacks, Queues, etc. These are all computer science topics and good to know, but unless you are working on high level stuff, you probably don’t have to know all of them. But those pesky interviewers will probably test you on them because they know most bootcamps don’t teach it and because they had to learn it when they got their BS in CS.

Heavy Petting

One of those terms, Big O Notation, is actually very useful to know. When you begin to program, you’re not thinking about how your program will scale if a few thousand or perhaps a million people start to use it. You just learn what a for loop is, then learn you can have nested for loops, and you think everything is grand! Not so fast Kemosabe. This is where Big O Notation and scaling come in. Let’s take a look at how you might write a function to double each element in an array of arrays.


function doubleMe(arrayOfArrays) {
  const doubledArrayOfArrays = [];

  for (let i = 0; i < arrayOfArrays.length; i++) {
    let placeholderArray = []
    for (let j = 0; j < arrayOfArrays[i].length; j++) {
      placeholderArray.push(arrayOfArrays[i][j] * 2);
    }
    doubledArrayOfArrays.push(placeholderArray)
  }

 return doubledArrayOfArrays;
}

doubleMe([[1,2,3], [4,5,6], [7,8,9]];  // [[2,4,6], [8,10,12], [14,16,18]]

This might look all fine and dandy, and when you first learn about nested for loops they might seem like the best thing since sliced bread! But let’s take a look at how this will scale.

We Have Lift Off

The length or size of our arrayOfArrays above is 3. However, since each element of the array is another array the function has to work that much more. Basically, for every item in the array (n for the input size), we have to do n more operations. So n * n == n^2 or O(n^2). The given example might be a little too on the nose being 3^2 is 9. It’s usually not that exact. You might ask, ‘So what’s the big deal? The function only has to run 9 times instead of 3’. Well, everything is groovy if the input is low, but what if it grows to 100 or 1,000 or 1,000,000. You start to get the point. With lower inputs, it’s not a big deal, but as the input grows, so does the time complexity of the function.

BigOn2

Weeeeeeeeeeeeeeeee!!!!

I’m Very Sensitive

Sorry if I got a little too excited. Let’s back up here a bit. Maybe I should start with O(1). Gayle Laakmann McDowell, author of a Cracking the Coding Interview, has a great video about Big O. It’s definitely worth a watch. She gives a great example about a problem South African programmers were having. Their internet connection was super slow and it was taking a long time to transfer data to team members in a different city. So they tried an experiment. They transferred the data to a usb drive and had a carrier pigeon (let’s call him Bob) deliver it to their work mates in the other city. At the same time they were transferring the data through their internet connection. The race between Bob and the internet. Guess who won?

If you said ‘BOB!’, then you are correct. So what does this have to do with Big O? Glad you asked! Bob’s flight in Big O terms is O(1). If it took Bob 30 minutes to get from one office to the other, then no matter what size the file is, it does not change the amount of time it takes him. Whether he’s flying with 10MB or 1TB, it still takes him 30 minutes. So O(1) is a program or function that takes the same amount of time to run no matter how large the input grows.

Time_Complexity

Bob is a low flying bird

Almost There

Revisiting our South African friends, as the size of the data they were transferring (over the internet) grew, the time it took to transfer grew by the same order. This would be O(n) and is linear in time and space. The green line in the graph above represents this. What would this look like as a function? Take my hand and let us find out.


function tripleMe(array) {
  const tripledArray = [];

  for (let i = 0; i < array.length; i++) {
    tripledArray.push(array[i] * 3);
  }

  return tripledArray;
}

tripleMe([1,2,3,4,5]);   // [3,6,9,12,15]

Each element of the array gets worked on once. If our array had 1,000,000 elements, our for loop would run 1,000,000 times. From an input of an array of 1 element to an input of an array with 1,000,000 elements, the time complexity a straight line.

Pillow Talk

There are definitely other elements of Big O to talk about and understand, but I’m spent. I gave a pretty good (in my humble opinion) performance overview of the basics. I hope it was as good for you as it was for me. Sweet dreams buttercup.