re-frame/docs/Using-Stateful-JS-Component...

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## Using Stateful JS Components
You know what's good for you, and you know what's right. But it
doesn't matter - the wickedness of the temptation is too much.
The JS world is brimming with shiny component baubles: D3,
Google Maps, Chosen, etc.
But they are salaciously stateful and mutative. And, you,
raised in a pure, functional home, with caring, immutable parents,
know they are wrong. But, my, how you still yearn for the sweet
thrill of that forbidden fruit.
I won't tell, if you don't. But careful plans must be made ...
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## Table Of Contents
- [The overall plan](#the-overall-plan)
- [Example Using Google Maps](#example-using-google-maps)
- [Pattern Discovery](#pattern-discovery)
- [Code Credit](#code-credit)
- [D3 Examples](#d3-examples)
- [Advanced Lifecycle Methods](#advanced-lifecycle-methods)
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### The overall plan
To use a stateful js component, you'll need to write two Reagent components:
- an **outer component** responsible for sourcing data via a subscription or r/atom or cursor, etc.
- an **inner component** responsible for wrapping and manipulating the stateful JS component via lifecycle functions.
The pattern involves the outer component, which sources data, supplying this data to the inner component **via props**.
### Example Using Google Maps
```cljs
(defn gmap-inner []
(let [gmap (atom nil)
options (clj->js {"zoom" 9})
update (fn [comp]
(let [{:keys [latitude longitude]} (reagent/props comp)
latlng (js/google.maps.LatLng. latitude longitude)]
(.setPosition (:marker @gmap) latlng)
(.panTo (:map @gmap) latlng)))]
(reagent/create-class
{:reagent-render (fn []
[:div
[:h4 "Map"]
[:div#map-canvas {:style {:height "400px"}}]])
:component-did-mount (fn [comp]
(let [canvas (.getElementById js/document "map-canvas")
gm (js/google.maps.Map. canvas options)
marker (js/google.maps.Marker. (clj->js {:map gm :title "Drone"}))]
(reset! gmap {:map gm :marker marker}))
(update comp))
:component-did-update update
:display-name "gmap-inner"})))
(defn gmap-outer []
(let [pos (subscribe [:current-position])] ;; obtain the data
(fn []
[gmap-inner @pos])))
```
Notes:
- `gmap-outer` obtains data via a subscription. It is quite simple - trivial almost.
- it then passes this data __as a prop__ to `gmap-inner`. This inner component has the job of wrapping/managing the stateful js component (Gmap in our case above)
- when the data (delivered by the subscription) to the outer layer changes, the inner layer, `gmap-inner`, will be given a new prop - `@pos` in the case above.
- when the inner component is given new props, its entire set of lifecycle functions will be engaged.
- the renderer for the inner layer ALWAYS renders the same, minimal container hiccup for the component. Even though the `props` have changed, the same hiccup is output. So it will appear to React as if nothing changes from one render to the next. No work to be done. React/Reagent will leave the DOM untouched.
- but this inner component has other lifecycle functions and this is where the real work is done.
- for example, after the renderer is called (which ignores its props), `component-did-update` will be called. In this function, we don't ignore the props, and we use them to update/mutate the stateful JS component.
- the props passed (in this case `@pos`) in must be a map, otherwise `(reagent/props comp)` will return nil.
### Pattern Discovery
This pattern has been independently discovered by many. To my knowledge,
[this description of the Container/Component pattern](https://medium.com/@learnreact/container-components-c0e67432e005#.3ic1uipvu)
is the first time it was written up.
### Code Credit
The example gmaps code above was developed by @jhchabran in this gist:
https://gist.github.com/jhchabran/e09883c3bc1b703a224d#file-2_google_map-cljs
### D3 Examples
D3 (from @zachcp):
- Blog Post: http://zachcp.org/blog/2015/reagent-d3/
- Code: https://github.com/zachcp/simplecomponent
- Example: http://zachcp.github.io/simplecomponent/
A different take on using D3:
https://gadfly.io/2016-10-22-d3-in-reagent.html
### Advanced Lifecycle Methods
If you mess around with lifecycle methods, you'll probably want to read Martin's explanations:
https://www.martinklepsch.org/posts/props-children-and-component-lifecycle-in-reagent.html