Fusion.lua

local function NumberEntry(labelText: string, defaultValue: number, onChanged: (value: number) -> (), parent: Instance)
	local text = Fusion.Value(tostring(defaultValue))
	local value = Fusion.Value(defaultValue)

	return Fusion.New("Frame") {
		AutomaticSize = Enum.AutomaticSize.X,
		BackgroundColor3 = Color3.fromRGB(54, 54, 54),
		Name = "Container",
		Parent = parent,
		Size = UDim2.fromOffset(200, 30),

		[Fusion.Cleanup] = Fusion.Observer(value):onChange(function()
			onChanged(value:get())
		end),

		[Fusion.Children] = {
			Fusion.New("UICorner") {
				CornerRadius = UDim.new(0, 8),
			},

			Fusion.New("UIListLayout") {
				FillDirection = Enum.FillDirection.Horizontal,
				HorizontalAlignment = Enum.HorizontalAlignment.Left,
				SortOrder = Enum.SortOrder.LayoutOrder,
			},

			Fusion.New("TextLabel") {
				BackgroundTransparency = 1,
				FontFace = Font.fromEnum(Enum.Font.Roboto),
				LayoutOrder = 0,
				Size = UDim2.fromScale(0.6, 1),
				Text = labelText,
				TextColor3 = Color3.fromRGB(147, 147, 147),
				TextScaled = true,
				TextXAlignment = Enum.TextXAlignment.Right,
			},

			Fusion.New("TextBox") {
				BackgroundTransparency = 1,
				FontFace = Font.fromEnum(Enum.Font.Roboto),
				LayoutOrder = 1,
				PlaceholderText = tostring(defaultValue),
				Size = UDim2.fromScale(0.4, 1),
				Text = Fusion.Computed(function()
					return tostring(text:get())
				end),

				TextColor3 = Color3.fromRGB(147, 147, 147),
				TextScaled = true,
				[Fusion.OnChange("Text")] = function(currentText)
					local number = GetNumberFromString(currentText)
					value:set(number)
					text:set(tostring(number))
				end,
			},

			Fusion.New("UIPadding") {
				PaddingBottom = UDim.new(0, 5),
				PaddingLeft = UDim.new(0, 5),
				PaddingRight = UDim.new(0, 5),
				PaddingTop = UDim.new(0, 5),
			},
		},
	}
end

return NumberEntry

Plasma.lua

local NumberEntry = Plasma.widget(function(labelText, defaultValue)
	local text, setText = Plasma.useState(tostring(defaultValue))
	local value, setValue = Plasma.useState(defaultValue)

	local textBox = Plasma.useInstance(function(ref)
		local textBox = Plasma.create("TextBox", {
			BackgroundTransparency = 1,
			FontFace = Font.fromEnum(Enum.Font.Roboto),
			LayoutOrder = 1,
			PlaceholderText = tostring(defaultValue),
			Size = UDim2.fromScale(0.4, 1),
			Text = tostring(text),
			TextColor3 = Color3.fromRGB(147, 147, 147),
			TextScaled = true,
			[ref] = "TextBox",
		})

		return Plasma.create("Frame", {
			AutomaticSize = Enum.AutomaticSize.X,
			BackgroundColor3 = Color3.fromRGB(54, 54, 54),
			Name = "Container",
			Size = UDim2.fromOffset(200, 30),
			Plasma.create("UICorner", {
				CornerRadius = UDim.new(0, 8),
			}),

			Plasma.create("UIListLayout", {
				FillDirection = Enum.FillDirection.Horizontal,
				HorizontalAlignment = Enum.HorizontalAlignment.Left,
				SortOrder = Enum.SortOrder.LayoutOrder,
			}),

			Plasma.create("TextLabel", {
				BackgroundTransparency = 1,
				FontFace = Font.fromEnum(Enum.Font.Roboto),
				LayoutOrder = 0,
				Size = UDim2.fromScale(0.6, 1),
				Text = labelText,
				TextColor3 = Color3.fromRGB(147, 147, 147),
				TextScaled = true,
				TextXAlignment = Enum.TextXAlignment.Right,
			}),

			textBox,
			Plasma.create("UIPadding", {
				PaddingBottom = UDim.new(0, 5),
				PaddingLeft = UDim.new(0, 5),
				PaddingRight = UDim.new(0, 5),
				PaddingTop = UDim.new(0, 5),
			}),
		})
	end)

	Plasma.useEffect(function()
		local currentTextBox = textBox.TextBox
		local connection = currentTextBox:GetPropertyChangedSignal("Text"):Connect(function()
			local number = GetNumberFromString(currentTextBox.Text)
			setValue(number)
			setText(tostring(number))
		end)

		return function()
			connection:Disconnect()
		end
	end, textBox.TextBox)

	return value
end)

return NumberEntry