What is the IsA event used for?

IsA() is used to check if an instance's ClassName is the same as what you specify. For example:

if object:IsA("BasePart") then

This will check if the object is a BasePart. You can find the ClassName of an instance in its properties. Here's some more information if you need it: https://www.robloxdev.com/api-reference/function/Instance/IsA

What is the IsA event used for? If you're looking to change multiple objects in a parent to something that you want it to be.

How could I use it? Well, if makes your script a lot neater. If you have multiple objects in a Folder, and you want all the specific objects to either destroy or do something you want it to. You would get all those specific objects in that.

Example:

for i, v in pairs(Folder:GetChildren()) do

    if v:IsA("BoolValue") then
        v:Destroy()
    end

end

Instance: IsA

Hoped this help alot!

What is IsA()

IsA() is a function(not a event). It takes only one parameter

Function Overview

Object:IsA(string className)

This returns a boolean. This boolean is if it is actually part of the class or if the object you are checking inherits from the class.

Function Example

local brick = game.Worksapce:WaitForChild("Baseplate")
local isAPart = brick:IsA("Part") -- Returns true

-- isABasepart true as well because Part 
-- inherits from the BasePart class
local isABasepart = brick:IsA("BasePart")

local isARemoteEvent = brick:IsA("RemoteEvent") -- Returns false

print("IsA Part:",isAPart) --> IsA Part: true
print("IsA BasePart:",isABasepart) --> IsA BasePart: true
print("IsA RemoteEvent:",isARemoteEvent) --> IsA RemoteEvent: false 

Pretty much Object:IsA("BasePart") is

local brick = game.Workspace:WaitForChild("Baseplate")
local isABasepart = brick:IsA("Part") or brick:IsA("Union") or brick:IsA("MeshPart")

This is an alternative to:

local brick = game.Worksapce:WaitForChild("Baseplate")
local isAPart = brick.ClassName == "Part" --true

-- When we check if our brick variable is equal to "BasePart" 
-- It will return false because in properties(find ClassName)
-- it would say Part
local isABasepart = brick.ClassName == "BasePart"

local isARemoteEvent = brick.ClassName == "RemoteEvent" -- Returns false

print("IsA Part:",isAPart) --> IsA Part: true
print("IsA BasePart:",isABasepart) --> IsA BasePart: false
print("IsA RemoteEvent:",isARemoteEvent) --> IsA RemoteEvent: false 

Use Cases

I find IsA() to play a decent role in a game. Let's say an example: We are iterating through a model. We have several bool values. Instead of manually coding for them to be true, you iterate the model.

Without IsA()

for _,child in next,script.Parent:GetChildren() do -- same as pairs(script.Parent:GetChildren())
    child.Value = true
end

The problem about the code snippet above is that we are assuming that the child we are currently at is a BoolValue.

What can we do to fix this code?

With IsA()

for _,child in next,script.Parent:GetChildren() do
    -- There wouldn't be an error because 
    -- we aren't assuming we are working with a BoolValue
    if child:IsA("BoolValue") then 
        child.Value = true
    end
end

With IsA(), we don't have to worry if our assumption, every child in the model is a BoolValue, making us error.

What if we had Parts,Unions and MeshParts in our model? Let's say we want to make them Transparent. We can easily do this by adding a elseif statement.

for _,child in next,script.Parent:GetChildren() do
    if child:IsA("BoolValue") then 
        child.Value = true
    -- Remember, Parts,Unions and Meshes inherit from the BasePart class
    elseif child:IsA("BasePart") then -- An alternative conditional
        child.Transparency = 1
    end
end

Conclusion

Pretty much IsA() can help you a little in you game development life. Hopefully you learned a lot from this answer!

isA is used to see what class name your object is.