Web components

Web components is a series of W3C specs that aim to give web developers the power to create custom reusable components. The specs that form part of the web components framework are: HTML templates, custom elements, shadow DOM and HTML imports. Together these standards give us the power to create, load and use custom components.

HTML Templates

HTML Templates allow you to specify templates that you can later reference with JS and insert where you see fit. Templates are an alternative to writing HTML strings inside your JS code. Instead of having to concatenate a bunch of strings to form an html snippet now you can write it in HTML inside a template tag and then just use its content.

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Building modular apps with Angular - Part 2

In a previous post I explained how to start modularizing Angular apps.

I’m going to improve the app I built in my example so it now lazy loads the modules it needs when you change routes. The end result will be the main page only downloading main.js and whenever you change to /yours or /mine, the respective file will be loaded with its corresponding dependencies. This should be an easy task, but angular makes it really complicated.

Lets try the obvious approach. First of all we need to change main to not load mine and yours:

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define([], function() {
  var app = angular.module('myApp', ['ngRoute']);
  app.config(['$routeProvider', function($routeProvider) {
    $routeProvider.otherwise({
      templateUrl: 'templates/main.html',
      controller: 'MainController'
    });
  }])
  .controller('MainController', function() {});

  angular.bootstrap(document.getElementsByTagName('html')[0], ['myApp']);
});
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Building modular apps with Angular

Building modular apps with Angular is not an easy task. Since I arrived into an Angular project a couple of months ago I’ve been struggling with our architecture, trying to make it modular in a way that makes sense, and it hasn’t been a walk in the park.

Lets try to build an example app to see what I’m talking about. For my example we are going to have a single page app with three screens:

  • Greetings screen – Contains links to mine and yours pages
  • Mine – Shows a list of my stuff and has a link to greetings page
  • Yours – Shows a list of your stuff and has a link to greetings page

These are the parts that will make our app:

  • App module
  • Greetings controller
  • Mine controller
  • Yours controller
  • Reusable list module
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Maximum length palindromic subsequence

Given a sequence of characters, find the longest palindromic sub-sequence. A sub-sequence is any sequence that can be formed by removing 0 or more characters from the given sequence. For example, the possible sub-sequences for ABC are:

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ABC
BC
C
B
AC
C
A
AB
B
A
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Bash productivity tips

See command history

When I want to find a command I used in the past, but I don’t remember I usually use vim to search for it:

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vim ~/.bash_history

This is useful because you get the whole list of commands in your history and all the power of vim to search for the command you are looking for. A faster way to show the list of the commands is with the history command:

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history
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Implementing Content Security Policy (CSP)

Content Security Policy is a browser feature that allows us to make our apps more secure by helping us prevent Cross Site Scripting(XSS) and content injection attacks. The way it does this is by giving us control over where resources will be loaded from and executed.

Even though CSP is supported by most browsers, you should always develop your apps thinking of the worst case scenario (The browser not supporting CSP). The golden security rule for web apps is: Filter input, escape output.

Enabling CSP requires us to configure our server to add a header to our document response. The most restrictive(and safest) value for this header would be:

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Content-Security-Policy: default-src 'none';
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The Fibonacci sequence

The Fibonacci sequence is a sequence of numbers starting with 0 and 1 and then adding the sum of the two last numbers at the end of the sequence:

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0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ...

The mathematical representation of the Fibonacci sequence is:

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F(n) = F(n-1) + F(n-2)
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Routing with angular

Angular’s ngRoute is useful when building single page apps with multiple views. It allows you to easily load a template into the screen and initialize the controller associated with it.

This is not only helpful to keep your code organized by having different controllers for different screens, but also gives your users a way to create bookmarks that associate a URL in the address bar with the current content of your app. This is a piece of functionality that has always been part of the web(links), so it is a good a idea to keep it there so users don’t run into unexpected behavior.

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Unique paths

A robot is located at the top-left corner of a m x n grid (marked ‘S’ in the diagram below). The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked ‘F’ in the diagram below). How many possible unique paths are there?

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+---+---+---+---+---+---+---+
| S |   |   |   |   |   |   |
+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |
+---+---+---+---+---+---+---+
|   |   |   |   |   |   | F |
+---+---+---+---+---+---+---+

The first idea that came to my mind after seeing this problem was to find all the combinations for two movements down and six movements to the right(»»»vv). I couldn’t remember of the top of my head the formula but after a little playing with pen and paper it came back to me. The formula is:

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Binary search

I was just going through the basics and I wanted to verify that I still knew how to do a binary search. If I remember correctly these are the steps:

– Set a left pointer at the beginning of the sorted array

– Set a right pointer at the end of the sorted array

– Calculate the middle between those two pointers(If there is no exact middle, truncate the number) and set the a middle pointer there

– Check if the middle is the number you are looking for. If it is return

– If the element at middle is greater than the element you are looking for set the left pointer to middle + 1

– If the element at middle is lower than the element you are looking for set the right pointer to middle – 1

– Repeat until the number is found or left is greater than right (not found)

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