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Errors & Messages

If your code isn't working properly, or if Fusion is malfunctioning, you may see some errors being printed to the output. Each message comes with a unique ID at the end.

On this page, you can learn more about any error messages you're receiving.

cannotAssignProperty

The class type 'Foo' has no assignable property 'Bar'.

This message shows if you try to assign a non-existent or locked property using the New function:

local folder = New "Folder" {
    DataCost = 12345,
    ThisPropertyDoesntExist = "Example"
}

Tip

Different scripts may have different privileges - for example, plugins will be allowed more privileges than in-game scripts. Make sure you have the necessary privileges to assign to your properties!

cannotConnectChange

The Frame class doesn't have a property called 'Foo'.

This message shows if you try to connect a handler to a non-existent property change event when using the New function:

local textBox = New "TextBox" {
    [OnChange "ThisPropertyDoesntExist"] = function()
        ...
    end)
}

cannotConnectEvent

The Frame class doesn't have an event called 'Foo'.

This message shows if you try to connect a handler to a non-existent event when using the New function:

local button = New "TextButton" {
    [OnEvent "ThisEventDoesntExist"] = function()
        ...
    end)
}

cannotCreateClass

Can't create a new instance of class 'Foo'.

This message shows when using the New function with an invalid class type:

local instance = New "ThisClassTypeIsInvalid" {
    ...
}

computedCallbackError

Computed callback error: attempt to index a nil value

This message shows when the callback of a computed object encounters an error:

local example = Computed(function()
    local badMath = 2 + "fish"
end)

invalidSpringDamping

The damping ratio for a spring must be >= 0. (damping was -0.50)

This message shows if you try to provide a damping ratio to a spring which is less than 0:

local speed = 10
local damping = -12345
local spring = Spring(state, speed, damping)

Damping ratio must always be between 0 and infinity for a spring to be physically simulatable.

invalidSpringSpeed

The speed of a spring must be >= 0. (speed was -2.00)

This message shows if you try to provide a speed to a spring which is less than 0:

local speed = -12345
local spring = Spring(state, speed)

Since a speed of 0 is equivalent to a spring that doesn't move, any slower speed is not simulatable or physically sensible.

mistypedSpringDamping

The damping ratio for a spring must be a number. (got a boolean)

This message shows if you try to provide a damping ratio to a spring which isn't a number:

local speed = 10
local damping = true
local spring = Spring(state, speed, damping)

mistypedSpringSpeed

The speed of a spring must be a number. (got a boolean)

This message shows if you try to provide a speed to a spring which isn't a number:

local speed = true
local spring = Spring(state, speed)

mistypedTweenInfo

The tween info of a tween must be a TweenInfo. (got a boolean)

This message shows if you try to provide a tween info to a tween which isn't a TweenInfo:

local tweenInfo = true
local tween = Tween(state, tweenInfo)

pairsDestructorError

ComputedPairs destructor error: attempt to index a nil value

This message shows when the destructor callback of a ComputedPairs object encounters an error:

local example = ComputedPairs(
    data,
    processor,
    function(value)
        local badMath = 2 + "fish"
    end
)

pairsProcessorError

ComputedPairs callback error: attempt to index a nil value

This message shows when the processor callback of a ComputedPairs object encounters an error:

local example = ComputedPairs(data, function(key, value)
    local badMath = 2 + "fish"
end)

springTypeMismatch

The type 'number' doesn't match the spring's type 'Color3'.

Some methods on spring objects require incoming values to match the types previously being used on the spring.

This message shows when an incoming value doesn't have the same type as values used previously on the spring:

local colour = State(Color3.new(1, 0, 0))
local colourSpring = Spring(colour)

colourSpring:addVelocity(Vector2.new(2, 3))

strictReadError

'Foo' is not a valid member of 'Bar'.

In Fusion, some tables may have strict reading rules. This is typically used on public APIs as a defense against typos.

This message shows when trying to read a non-existent member of these tables.

unknownMessage

Unknown error: attempt to index a nil value

If you see this message, it's almost certainly an internal bug, so make sure to get in contact so the issue can be fixed.

When Fusion code attempts to log a message, warning or error, it needs to provide an ID. This ID is used to show the correct message, and serves as a simple, memorable identifier if you need to look up the message later. However, if that code provides an invalid ID, then the message will be replaced with this one.

unrecognisedChildType

'number' type children aren't accepted as children in `New`.

This message shows when attempting to pass something as a child which isn't an instance, table of instances, or state object containing an instance (when using the New function):

local instance = New "Folder" {
    [Children] = {
        1, 2, 3, 4, 5,

        {true, false},

        State(Enum.Material.Grass)
    }
}

Note

Note that state objects are allowed to store nil to represent the absence of an instance, as an exception to these rules.

unrecognisedPropertyKey

'number' keys aren't accepted in the property table of `New`.

When you create an instance in Fusion using New, you can pass in a 'property table' containing properties, children, event and property change handlers, etc.

This table is only expected to contain keys of two types:

  • string keys, e.g. Name = "Example"
  • a few symbol keys, e.g. [OnEvent "Foo"] = ...

This message shows if Fusion finds a key of a different type, or if the key isn't one of the few symbol keys used in New:

local folder = New "Folder" {
    [Vector3.new()] = "Example",

    "This", "Shouldn't", "Be", "Here"
}