React

Is a library for building UIs.

Components, instances, and elements

Components
- main building blocks, contain logic and markup (in JSX) needed to render a part of an application
- can be divided in into Presentational and Container (aka smart and dumb) Components
Instances - instances of a Component, just like instances of a class
Elements
- "plain object describing a component instance or DOM node and its desired properties."
- An Element "takes props as an input, and returns an element tree as the output"
- they usually belong in the the render() method of a Component
- it looks like this: {type: someType, props: someProps}
- type can be a Component (BigButton) or a name of a DOM node ('button')
- props key contains a children key, which can be a text node or an array of Elements
```
// an element as plain object (theory):
{
  type: Button,
  props: {
    children: 'Sign up'
  }
}
// and in JSX (practice):
<Button>Sign up</Button>
```

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