mediumtypeof type queries
What does `BoxCtor` represent, and which expression below is therefore valid?
class Box {
value = 0;
static make() { return new Box(); }
}
type BoxCtor = typeof Box;why this works
Built for TypeScript mastery, not memorisation.
Every question is hand-checked, every answer comes with an explanation, and your progress builds into a clear picture of where you stand.
The snippet is on the page
Every TypeScript question shows its code before you answer, so you are reading real TypeScript, not a description of it.
A written explanation, always
Once you attempt a question you get the reasoning, not just a tick. That matters most on TypeScript, where expect inference puzzles: conditional types, mapped types, variance on function parameters, and when a union distributes.
Your weak topics, named
Progress is tracked per topic across the 44 TypeScript topics, so revision points at the gaps instead of the whole list.
faq
Things people ask.
How many TypeScript MCQs are on Journey Uncommon?
606 TypeScript questions right now: 125 easy, 219 medium and 262 hard. That number is read straight from the question table when this page is built, so it is never a rounded marketing figure.
Do I need an account to read the TypeScript questions?
No. Every TypeScript question, including its code snippet, its difficulty and its topic, is readable without signing in. You need a free account only to submit an answer, see which option is correct, and read the worked explanation. We keep it that way so the platform stays honest about what you actually got right.
What do TypeScript interviewers actually test?
Expect inference puzzles: conditional types, mapped types, variance on function parameters, and when a union distributes. A large share of questions are literally 'what is the inferred type here'.
Which TypeScript topics are covered?
44 distinct topics are tagged on the TypeScript questions, including type annotations, hand-rolled utility types, primitive types, ESM CJS interop, conditional-type distribution, control-flow analysis pitfalls. The topic labels come from the questions themselves, so the list matches what you will actually be asked.
Is TypeScript practice free?
Yes. Reading is free and unlimited. A free account unlocks answering, explanations and progress tracking. Pro (₹199 per month) adds AI explanations and AI-graded guesstimates on top; it is not needed to practise TypeScript MCQs.
Where is TypeScript used in real jobs?
Product engineering teams that outgrew plain JavaScript, design-system work, and any codebase large enough to need refactor safety.
What a TypeScript question here actually looks like
These are 12 of the 606 TypeScript questions in the library, pulled live from the question table. The snippet, the difficulty and the topic are all here. The answer options and the explanation are not. Those need a free account.
Expect inference puzzles: conditional types, mapped types, variance on function parameters, and when a union distributes. A large share of questions are literally 'what is the inferred type here'.
Sample TypeScript MCQs
hardarrays and tuples
What is the type of x?
const arr: number[] = [1,2,3];\nconst x = arr[0]; // with noUncheckedIndexedAccesshardtemplate literal types
What is X?
type X = `${Capitalize<"foo">}Bar`;hardprimitive types
What is X?
type X = string & number;hardtypeof type queries
What is the type of f?
const f = (x: number) => x + 1;mediumprimitive types
What is the type of x?
let x = 5;hardconditional-type distribution
What is X?
type X = Exclude<"a"|"b","a"|"b">;hardconditional-type distribution
How does TypeScript handle the `never` member when this distributive conditional is applied to a union containing `never`?
type ToArray<T> = T extends unknown ? T[] : never;
type R = ToArray<string | never>;easytype annotations
What does the type annotation on the `point` parameter require a caller to pass?
function distance(point: { x: number; y: number }): number {
return Math.sqrt(point.x ** 2 + point.y ** 2);
}mediumgeneric constraints
`keyof` over a union of object types returns the keys common to every member. What is `Result`?
type Result = keyof ({ a: 1; b: 2 } | { b: 3; c: 4 });hardkeyof and indexed access
What is the type of x?
const arr = ["a", "b"] as const;\ntype X = typeof arr[number];mediumuser-defined type guards
Both functions test the same condition, but only one narrows. Why does `an2.bark()` fail to compile?
interface Animal { type: string }
interface Dog extends Animal { type: "dog"; bark(): void }
function isDog(a: Animal): a is Dog { return a.type === "dog"; }
function looksDog(a: Animal): boolean { return a.type === "dog"; }
declare const an2: Animal;
if (looksDog(an2)) {
an2.bark();
}Sign in to answer
Everything above is free to read. Answering needs a free account.
We keep the correct answer, the explanation and the scoring behind sign-in so the platform stays honest, which is why the correct option and the worked explanation for every TypeScript question stay behind a free account. Signing in is free and takes a few seconds.
Where TypeScript shows up
Product engineering teams that outgrew plain JavaScript, design-system work, and any codebase large enough to need refactor safety.