Concepts Summary

A summary of all the concepts covered during the crash course.

Source

A source of data.

Stores a single value that can be updated.

Created with source().

Derived Source

A new source composed of other sources.

Created with a plain function or with derive().

Effect

Anything that happens in response to a source update.

Created with effect().

Stable Scope

One of the two types of Vide scopes.

Created by:

root()
untrack()
switch()
indexes()

Stable scopes do not track sources and never rerun.

New stable or reactive scopes can be created within a stable scope.

Reactive Scope

Created by:

effect()
derive()

Reactive scopes do track sources and will rerun when those sources update.

Reactive scopes cannot be created within a reactive scope, but stable scopes can.

Scope Owners

A scope created within another scope is owned by the other scope, with the exception of the scope created by root().

When a scope is rerun or destroyed, all scopes owned by it are automatically destroyed.

root() creates a stable scope with no owner, instead it is destroyed manually.

Cleanup

Arbitrary code to run whenever a stable or reactive scope is rerun or destroyed.

Queue a function to run using cleanup().

Reactive Graph

The combination of stable and reactive scopes can viewed graphically, called a reactive graph. This can be a more intuitive way to think of the relationships between effects and the sources they depend on.

Code

local count = source(0)

root(function()
    local text = derive(function()
        return "count: " .. text()
    end)

    effect(function()
        print(text())
    end)
end)

Graph resulting from code

%%{init: {
    "theme": "base",
    "themeVariables": {
        "primaryColor": "#1B1B1F",
        "primaryTextColor": "#fff",
        "primaryBorderColor": "#1B1B1F",
        "lineColor": "#79B8FF",
        "tertiaryColor": "#161618",
        "tertiaryBorderColor": "#1C1C1F"
    }
}}%%

graph LR

subgraph root
    text --> effect
end

count --> text

Notes:

Since count is a source, not an effect, it can exist outside of scopes.
An update to count will cause text to rerun, which then causes effect to rerun.
When the root scope is destroyed, text and effect will be destroyed alongside it, since they are owned by it. count will be untouched and future updates to count will have no effect.

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