Formatting interview questions

Build a countdown timer that ticks down from a start time and can start, pause, and reset.

Implement a function that joins an array of strings into a grammatical list with commas and a conjunction.

Implement a function that wraps occurrences of a search term within a string in highlight markup.

Implement a utility that conditionally joins class name arguments into a single space-separated string.

Build a currency converter with two linked amount fields that recompute from an exchange rate.

Build a 7-segment style digital clock that updates to display the current time.

Implement a function that serializes a tree-shaped object into a pretty-printed HTML string with indentation.

Build a translation engine with nested key lookup, variable interpolation, pluralization, and locale fallback.

Implement a function that converts a JavaScript value into its JSON string representation.

Round, floor, and ceil a number to N decimal places without the classic floating-point drift — 1.005 must round to 1.01, not 1.00.

Build a cart where quantity changes update line totals and a grand total live.

Build a stopwatch widget that measures elapsed time with start, stop, and reset controls.

Implement a template renderer that substitutes Mustache-style placeholders with values from a data object.

Group a number's integer digits with separators — 1234567 to 1,234,567 — handling decimals, negatives, and a custom separator.

Implement lodash truncate — cut a string to a maximum length, append an ellipsis, and optionally break on the last word boundary before the limit.

Extend the classNames utility to dedupe class names and resolve function arguments lazily.

Spell out a non-negative integer in English words — break it into groups of three digits and name each group with its scale word.

Implement JSON.stringify with full spec support including replacer, indentation, and circular reference detection.

Implement a function that converts a list of styled text ranges into a canonical, properly nested HTML string.