I’d change it to a loop, like such-
while wait() do
script.Parent.Size = UDim2.new(boss.Health/ boss.MaxHealth, 0, 1, 0)
end
No you should not do this. While wait() loops are incredibly inefficient and should not be used whenever possible (99% of the time).
I think it depends on what you’re using the loop for. But I don’t really know
Property changed signal works as intended. Your code would also not work after the NPC died as the boss no longer exists. Plus, you are running that code constantly, which is a waste of resources. By using propertychangedsignal, you are only running the code when it has to run.
Hey, are there any errors in the log? If not, it is likely because the npc was in the workspace on start. Try killing it and seeing if it works the next time around.
Like Official_MrBob101 said, loops aren’t great but try this-
while wait() do
if game.Workspace:WaitForChild(“NPC”) then
local boss = game.Workspace:WaitForChild(“NPC”):WaitForChild(“Humanoid”)
script.Parent.Size = UDim2.new(boss.Health/ boss.MaxHealth, 0, 1, 0)
end
end
Again this wont work. When the NPC dies, it will be reinstanced into the game. Again a while loop is not needed here and is incredibly inefficient.
-This thing works but, Do I need to kill it first to make the healthbar works?
-Also when it respawn the greenbar doesnt appear, it appears only when the npc takes damage.
(Im sorry, Im new in programming)
No that is ok! I thought this would happen. Here is the updated code, which should work. Good luck 
local boss = workspace:WaitForChild("NPC"):WaitForChild("Humanoid") --We need to run the code without a property changed signal for the first time it is in the game
script.Parent.Size = UDim2.new(boss.Health/ boss.MaxHealth, 0, 1, 0)
local signal = boss:GetPropertyChangedSignal("Health"):Connect(function()
script.Parent.Size = UDim2.new(boss.Health/ boss.MaxHealth, 0, 1, 0)
end)
local deathsig = boss.Humanoid.Died:Connect(function()
signal:Disconnect()
end)
deathsig:Disconnect()
boss = nil
workspace.DescendantAdded:Connect(function(des)
if des.Name == "NPC" then
local boss = des:WaitForChild("Humanoid")
script.Parent.Size = UDim2.new(boss.Health/ boss.MaxHealth, 0, 1, 0)
local signal = boss:GetPropertyChangedSignal("Health"):Connect(function()
script.Parent.Size = UDim2.new(boss.Health/ boss.MaxHealth, 0, 1, 0)
end)
local deathsig = boss.Humanoid.Died:Connect(function()
signal:Disconnect()
end)
deathsig:Disconnect()
end
end)i tested my loop in my own studio world and it works completely fine with no flaws.
Using that type of loop is incredibly inefficient as I have said multiple times. You should rely on a robust method for handling this sort of stuff. Just because it is easy to do doesn’t mean it is the best way. And just because it works fine once does not mean it will always be fine. :WaitForChild() is only meant to be used when needed, so running it every possible tick in that form of loop is bad practice and slow.
You’re right but if it has no flaws there’s no reason to not try it.
it said nil
Try removing the line boss = nil which I had below it.
i’ll leave you two to it
30 charssss
You want to provide the most insightful feedback with scripting support. This person is a learner, so it is best to give them advice that will set them up well. If I were to tell them to do what you are suggesting, they will then use that method in the future. Unbeknownst to them, they won’t realize it is madly inefficient and when making a more complex game, they could suffer from severe performance issues. That is why it is important to not take the quick route when providing a suggestion.
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No problem and good luck!
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Where did you get the gui from?