vide/docs/tut/crash-course/5-effect.md
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# Effects
Effects are functions that are ran in response to source updates. They are
A source and effect is analogous to a signal and connection.
Effects are created using `effect()`.
```luau
local source = vide.source
local effect = vide.effect
local count = source(0)
effect(function()
print("count: " .. count())
end)
-- "count: 0" printed
count(1)
-- "count: 1" printed
```
Any source read inside an effect is tracked and will rerun the effect when
that source is updated.
Derived sources are also tracked, it doesn't matter how deeply nested
inside a function a source is.
```luau
local source = vide.source
local effect = vide.effect
local count = source(1)
local doubled = function()
return count() * 2
end
effect(function()
print("doubled count: " .. doubled())
end)
-- "doubled count: 2" printed
count(2)
-- "doubled count: 4" printed
```
If a source is updated with the same value it already had, it will not rerun
effects depending on it.