95 lines
4.3 KiB
Markdown
95 lines
4.3 KiB
Markdown
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## Using Stateful JS Components
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You know what's good for you, and you know what's right. But it
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doesn't matter - the wickedness of the temptation is too much.
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The JS world is brimming with shiny component baubles: D3,
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Google Maps, Chosen, etc.
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But they are salaciously stateful and mutative. And, you,
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raised in a pure, functional home, with caring, immutable parents,
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know they are wrong. But, my, how you still yearn for the sweet
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thrill of that forbidden fruit.
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I won't tell, if you don't. But careful plans must be made ...
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### The overall plan
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To use a stateful js component, you'll need to write two Reagent components:
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- an **outer component** responsible for sourcing data via a subscription or r/atom or cursor, etc.
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- an **inner component** responsible for wrapping and manipulating the stateful JS component via lifecycle functions.
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The pattern involves the outer component, which sources data, supplying this data to the inner component **via props**.
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### Example Using Google Maps
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```cljs
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(defn gmap-inner []
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(let [gmap (atom nil)
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options (clj->js {"zoom" 9})
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update (fn [comp]
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(let [{:keys [latitude longitude]} (reagent/props comp)
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latlng (js/google.maps.LatLng. latitude longitude)]
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(.setPosition (:marker @gmap) latlng)
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(.panTo (:map @gmap) latlng)))]
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(reagent/create-class
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{:reagent-render (fn []
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[:div
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[:h4 "Map"]
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[:div#map-canvas {:style {:height "400px"}}]])
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:component-did-mount (fn [comp]
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(let [canvas (.getElementById js/document "map-canvas")
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gm (js/google.maps.Map. canvas options)
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marker (js/google.maps.Marker. (clj->js {:map gm :title "Drone"}))]
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(reset! gmap {:map gm :marker marker}))
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(update comp))
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:component-did-update update
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:display-name "gmap-inner"})))
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(defn gmap-outer []
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(let [pos (subscribe [:current-position])] ;; obtain the data
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(fn []
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[gmap-inner @pos])))
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```
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Notes:
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- `gmap-outer` obtains data via a subscription. It is quite simple - trivial almost.
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- 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)
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- 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.
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- when the inner component is given new props, its entire set of lifecycle functions will be engaged.
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- 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.
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- but this inner component has other lifecycle functions and this is where the real work is done.
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- 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.
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- the props passed (in this case `@pos`) in must be a map, otherwise `(reagent/props comp)` will return nil.
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### Pattern Discovery
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This pattern has been independently discovered by many. To my knowledge,
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[this description of the Container/Component pattern](https://medium.com/@learnreact/container-components-c0e67432e005#.3ic1uipvu)
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is the first time it was written up.
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### Code Credit
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The example gmaps code above was developed by @jhchabran in this gist:
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https://gist.github.com/jhchabran/e09883c3bc1b703a224d#file-2_google_map-cljs
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### D3 Examples
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D3 (from @zachcp):
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- Blog Post: http://zachcp.org/blog/2015/reagent-d3/
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- Code: https://github.com/zachcp/simplecomponent
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- Example: http://zachcp.github.io/simplecomponent/
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### Advanced Lifecycle Methods
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If you mess around with lifecycle methods, you'll probably want to read Martin's explanations:
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https://www.martinklepsch.org/posts/props-children-and-component-lifecycle-in-reagent.html
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