JavaScript and TypeScript interviews

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Timed assessment

12 practical questions
60 minutes
Mid level

Questions are drawn from a bank of 36. Your report includes a skill breakdown and lessons to practice next.

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Practice interviews

Junior tasks cover the fundamentals. Mid and senior tasks add debugging, changing requirements and review decisions.

Position

10 interviews

Software engineer
Junior
20 min

Independent dispatch counters

Cedar Dispatch starts two independent ticket counters at 65 and 85. Call them in the order first, second, first, second. Return the four issued numbers. The factory must retain private state.

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Skills and rubricIndependent dispatch counters

Each closure retains its own next number; interleaving two counters cannot share state.
Traces one concrete example before coding.
Checks an empty input or the named boundary with an expected result.

Backend engineer
Junior
20 min

Stable loading-bay names

Juniper Freight accepts names beginning with the exact prefix depot65. Return matching names once each in first-seen order. Keep case-sensitive identity.

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Skills and rubricStable loading-bay names

The result contains each exact name once, in the order of its first accepted occurrence.
Traces one concrete example before coding.
Checks an empty input or the named boundary with an expected result.

Frontend engineer
Junior
20 min

Detached account labels

Orchard Billing has an account prefix account65. Bind its label method before calling it without an object receiver. Return the label for code.

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Skills and rubricDetached account labels

A detached method needs an explicit receiver; the account object remains the source of its label.
Traces one concrete example before coding.
Checks an empty input or the named boundary with an expected result.

Software engineer
Mid
30 min

Media notification order

Marble Media needs the execution trace for a local notification: append sync65, queue a promise append, append end, await one resolved promise, then append resumed. Prefix every marker with the supplied channel. Return the trace.

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Skills and rubricMedia notification order

Synchronous appends happen before queued promise callbacks, and the await continuation follows callbacks already queued.
Explains the hidden boundary and both misconceptions.
Describes how the language mechanism preserves the function contract.

Backend engineer
Mid
30 min

Scheduling payload guards

Willow Scheduling receives JSON. Parse it as unknown, then return a string code from an object, or missing65 for malformed JSON, null, arrays, or any other shape.

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Skills and rubricScheduling payload guards

Only an object with a string code reaches the typed accessor; null and invalid JSON return the fallback.
Explains the hidden boundary and both misconceptions.
Describes how the language mechanism preserves the function contract.

Frontend engineer
Mid
30 min

Typed depot projections

Pine Transit uses a generic pick helper. Implement getField<T,K extends keyof T> with result T[K], then return the label field of a route built from code with prefix route65.

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Skills and rubricTyped depot projections

The key is constrained to keyof T and the result preserves the selected property type T[K].
Explains the hidden boundary and both misconceptions.
Describes how the language mechanism preserves the function contract.

Software engineer
Mid
30 min

Retail import validation

Copper Retail imports a JSON array of finite numbers. Return their sum plus the configured opening balance 65, or invalid for malformed JSON and invalid members. Empty arrays return the opening balance as text.

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Skills and rubricRetail import validation

Malformed JSON, a nonarray root and nonfinite or nonnumeric members do not become valid totals.
Explains the hidden boundary and both misconceptions.
Describes how the language mechanism preserves the function contract.

Backend engineer
Senior
40 min

Bounded shipment attempts

Harbor Shipping supplies attempt outcomes where true means success. Return the one-based successful attempt, or zero when no success occurs in the first 65 attempts. Later outcomes are outside the retry budget.

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Skills and rubricBounded shipment attempts

The first success stops retries, and the maximum attempt count includes the initial attempt.
The timeout does not prove failure. I need an idempotency key and a reconciliation path before retrying, or a second successful charge could duplicate the side effect.
States which additional guarantee the changed requirement would need.

Frontend engineer
Senior
40 min

Immutable route patching

Meadow Travel patches a flat route record. Return a JSON object with original and updated records after setting zone to zone65. Do not mutate the original record. Input and output values are strings.

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Skills and rubricImmutable route patching

A patch changes the returned object while the original object keeps every original own value.
One spread copies only the outer object. I copy the address at the changed path too; otherwise the returned and original objects still share the nested address reference.
States which additional guarantee the changed requirement would need.

Software engineer
Senior
40 min

One-use booking subscriptions

Fern Booking registers a once listener. The listener records event plus 65 and recursively emits the next event. Return recorded values after starting with value. A once listener must run only once, even with reentry.

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Skills and rubricOne-use booking subscriptions

A once listener is removed before invocation so reentrant emission cannot invoke it again.
I define snapshot semantics: the current emission iterates a copy of its listener list, and additions take effect on later emissions. This prevents order from depending on array mutation during traversal.
States which additional guarantee the changed requirement would need.

Choose your character

JavaScript and TypeScript interviews

Timed assessment

Practice interviews

Independent dispatch counters

Stable loading-bay names

Detached account labels

Media notification order

Scheduling payload guards

Typed depot projections

Retail import validation

Bounded shipment attempts

Immutable route patching

One-use booking subscriptions

Interview Hub access

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