Conditionals

• ? : : the only branching construct
• ?? : reacts only to null/undefined, not a general conditional
• Playground

Operator	Effect
? :	the only branching construct
??	reacts only to null/undefined, not a general conditional

? : : the only branching construct

The condition must be a boolean; the result type is the union of both branches. Ternaries nest to express ladders — indentation is free-form.

tier: user.points >= 100 ? "gold"
    : user.points >= 50 ? "silver"
    : "bronze"

?? : reacts only to null/undefined, not a general conditional

?? is not a general conditional — it only reacts to null/undefined, while ? : branches on any boolean.

displayName: user.nickname ?? user.firstName
badge: user.verified ? "verified" : "unverified"

Playground

Mapping✔Playground ↗

input user: { points: number }

map {
  tier: user.points >= 100 ? "gold" : "standard",
}

input user: { points: number } map { tier: user.points >= 100 ? "gold" : "standard", }

Input JSON

{ "points": 132 }

{ "points": 132 }

Output

{
  "tier": "gold"
}

inferred type{ tier: "gold" | "standard" }

Note the inferred type of tier: "gold" | "standard", not just string.

Next: Arrays.