Today I Learned

TIL, 2018-04-30, React hydrate and studying patterns gem.

Musings, JS/React

  • What’s the difference between hydrate() and render() in React 16?If you call hydrate() on a node that already has this server-rendered markup, React will preserve it and only attach event handlers, allowing you to have a very performant first-load experience.
  • Window, The window object:
    • window represents a window containing a DOM document. document points to the DOM document loaded in that window.
    • You can do window.scrollTo({ top: 100, behavior: 'smooth'}) if you really wanted to do some scrolling from Inspect Element.
    • Relative: window.scrollBy(), window.scrollByLines(), and window.scrollByPages().
    • The primary object of a browser, so you don’t do window.alert(), you just do alert().
    • You can use it to get information re: the user’s window.
  • HTML Dataset
    • Allows to read/write custom data-* attributes on the element.
    • The dataset property can be read, but not written, you write on the properties/attributes inside.
<div id="user" data-id="1234567890" data-user="johndoe" data-date-of-birth>John Doe</div>

let el = document.querySelector('#user');

// == 'user'
// === '1234567890'
// el.dataset.user === 'johndoe'
// el.dataset.dateOfBirth === ''
  • Splitting big components:
    • Split the render() method: const PanelHeader, const PanelBody.
    • Pass React elements as props: For comments, one component to serve as a template, and one component to figure out what to fill metadata and possible actions (like, reply, and delete)
    • Higher-order components. Ex: Add analytics to a specific component.
  • Moment: 16kb, but really at lot more convenient than manually manipulating dates.



  • Hydration: to get some information from outside sources.
  • A: API call/AJAX via Axios or Fetch. Pro: secure, con: additional HTTP request.
  • B: Pass data via window object.
  • Pass data via attribute on parent node.


  • This can be used at the top level of you app and as an escape hatch to get outside the React model if you need to.

Functional Stateless Components in React


  • Destructuring in functional stateless components:
    • const Username = ({ username }) => <p>The logged in user is: {username}</p>;
  • Simplicity: You know that an FSC is just props in, rendered UI out. For a class component, you still have to scan through to see what lifecycle methods it is using.
  • FSCs offer visual cues that a component is just taking some props and rendering output. If you have a class component, you have to read through the code to see if it deals with state.
  • The less stateful component your app has, the better. They are easier to test and you can pass them as props and assert on their output.
  • Because it’s hard to convert an FSC to a stateful component, you come to appreciate it because it makes you think about if you want to add state to a component.
  • Easy to create styling.

Musings, Ruby

  • update_columns vs update_attributes: update_columns, because it skips callbacks, is faster than update_attributes by 50%, but you can update_attributes with multiple columns and that would sort of be the same as updating with one column (it makes sense, since both just do an UPDATE statement under the hood anyway).
  • jeweler and juwelier gem exist for creating Ruby gems.
  • Studying this gem, and specifically the Query pattern, things I found:
    • def*args); new(*args).call; end pattern to do class method as instance method, I’ve also implemented this in the past, but you have to remember the splat because of nil errors.
    • tap is used to modify an object

This project is maintained by daryllxd