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80 lines
2.3 KiB
Markdown
80 lines
2.3 KiB
Markdown
# Root Reactive Scopes
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Reactive scopes cannot be created on their own - they must be created within
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another reactive scope so that it can be tracked and later destroyed when it is
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no longer needed.
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This is the purpose of `mount()`, which creates an initial "root", or
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"top-level" reactive scope, which all other reactive scopes, such as
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ones created by `effect()`, can stem from.
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When this root reactive scope is destroyed, it will ensure all other reactive
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scopes created within it are also destroyed, ensuring everything is cleaned up
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properly.
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```lua
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local source = vide.source
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local effect = vide.effect
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local function App()
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local count = source(0)
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effect(function()
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print(count())
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end)
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end
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App() -- will error since effect() was not called within a reactive scope
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vide.mount(App) -- works!
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```
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Mounting returns a function that when called will destroy its reactive scope,
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along with any other reactive scopes created inside it.
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```lua
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local unmount = mount(App)
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unmount()
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```
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Vide's reactivity can be represented graphically, as a *reactive graph*.
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The reactive graph for the above example looks like so:
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```mermaid
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%%{init: {
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"theme": "base",
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"themeVariables": {
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"primaryColor": "#1B1B1F",
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"primaryTextColor": "#fff",
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"primaryBorderColor": "#1B1B1F",
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"lineColor": "#79B8FF",
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"tertiaryColor": "#161618",
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"tertiaryBorderColor": "#161618"
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}
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}}%%
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graph
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subgraph root
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direction LR
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count --> effect
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end
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```
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When the root reactive scope created by `mount()` is destroyed, the `effect`
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scope will also be destroyed since it was created within it.
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This is important because you may have an effect that updates the property of a
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UI instance, meaning the effect is referencing and holding that instance in
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memory. The effect being destroyed will remove this reference, allowing the
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instance to be garbage collected.
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You don't need to worry about ensuring all your effects are created within a
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root reactive scope, since you should be creating all your UI and corresponding
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effects within a top-level `mount()` call that puts all your UI together. So it
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is safe to assume that any effect you create will be created under this top
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level scope. Vide will prevent you from accidently doing otherwise anyways.
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