What's the difference between parent.child, parent:WaitForChild, parent:FindFirstChild, parent[childname]

I’m having some trouble choosing between the methods of getting children from the title. Could someone explain what each of them does and which should I use when?
Thanks

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Well, Parent.Child is basically the same as Parent[ChildName], and will error out if it doesn’t exist. FindFirstChild will look for the Child and not error out if it doesn’t exist. WaitForChild will yield until it finds the child.

For more details on each one, you can check out these links.

https://developer.roblox.com/en-us/api-reference/function/Instance/WaitForChild

https://developer.roblox.com/en-us/api-reference/function/Instance/FindFirstChild

https://developer.roblox.com/en-us/api-reference/property/Instance/Parent

Oh thanks! In that case why doesn’t this line work?
itemgui.Parent = toolbar[tostring(firstslot)]
firstslot is a number btw

We would need more context, are there any errors?

yes it outputs this error [24 is not a valid member of Frame]

There is nothing in Frame called “24”.

Parent.Child
The regular path used in the game-tree. Throws an error if the instance doesn’t exist.

Parent["Child"]
Same as above, however, this method allows for blankspaces.

Parent:WaitForChild("Child")
Same as the first method, however, this will yield until the child exists.

Parent:FindFirstChild("Child")
Same as the first method, however, it won’t error if the instance doesn’t exist, it will instead return nil.


As for the issue you provided, there is no instance named "24"under the toolbar parent. In the right context this can be resolved by using WaitForChild(), since the child might not yet have loaded.

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It’s important to note that this will cause problems if the child name conflicts with one of parent’s methods or properties (script.Clone, for example.) It’s always possible for new methods/properties to be added in the future, so I recommend FindFirstChild if you want your game to be robust.

It’s also important to be careful when accessing children of the Workspace or Players services by name, because a player could join with a conflicting name and cause errors. I’ve seen scripts that use workspace[player.Name], even though this will error if the player’s name is something like "FindPartOnRay" (or any of the nearly 80 members found here).

FindFirstChild may have similar problems this way, for example a player named "Camera" could theoretically cause problems even if you use workspace:FindFirstChild("Camera"). Player characters can also interfere with your instances in the workspace that you need to access, for example instead of workspace.HouseModels, I would recommend using something players cannot have as a username like workspace._HouseModels.

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