Condition Flow

if, elseif, else

Condition flow is how you make decisions in your code. The most fundamental tool for that is the if statement:

local score = 85

if score >= 90 then
    print("A")
elseif score >= 80 then
    print("B")
elseif score >= 70 then
    print("C")
else
    print("F")
end

Luau reads through each condition from top to bottom and runs the first block that's true. If none match, it falls through to else. You can have as many elseif branches as you need, and else is always optional.

if Expressions

Sometimes you just want to assign one of two values based on a condition. The if expression lets you do that inline, without writing a full if block:

local age = 20
local status = if age >= 18 then "adult" else "minor"
print(status) -- adult

The syntax is if condition then valueIfTrue else valueIfFalse. It's Luau's answer to the ternary operator you might've seen in other languages. Clean and readable.

The and/or Trick

Before if expressions existed in Luau, there was a pattern borrowed from Lua to achieve the same thing using and and or:

local age = 20
local status = age >= 18 and "adult" or "minor"
print(status) -- adult

Here's how it works — and returns the second value if the first is truthy, otherwise it returns the first. Then or returns the first value if it's truthy, otherwise the second. Chained together, it behaves like a ternary.

It works well in most cases, but it has one gotcha — if the "true" value is false or nil, the whole thing breaks:

local value = true and false or "fallback"
print(value) -- "fallback" (wrong! we wanted false)

So if you're on Luau, just use if expressions — they're safer and more readable. But you'll likely run into the and/or pattern in older Lua code or community projects, so it's good to know what it's doing.