Object Methods interview questions

Implement a function that consolidates rows sharing the same user into a single grouped record.

Implement a function that builds an object from an array of [key, value] pair tuples.

Implement a function that returns the number of declared parameters of a given function.

Implement a jQuery-style helper that gets or sets inline CSS properties on a DOM element.

Implement lodash keyBy — index a collection into an object keyed by an iteratee's return, keeping the last item for each key.

Implement a function that returns a new object with every value transformed by a mapper callback.

Implement Object.entries — return an object's own enumerable string-keyed [key, value] pairs in insertion order.

Implement Object.fromEntries — build an object from any iterable of [key, value] pairs, with later keys winning.

Implement a function that returns the element count of any collection — array, string, object, Map, or Set.

Implement a set of helper functions that report the primitive type of any JavaScript value.

Implement a function that returns a new object with every key converted to camelCase, recursing into nested objects.

Implement a simplified cva that builds class names from base styles, variant tables, and default values.

Implement a function that returns a deep copy of an object with all falsy values stripped from nested structures.

Implement a function that checks whether an object satisfies a source schema of predicate validators.

Implement a wrapper that intercepts console.log calls and records their arguments for later inspection.

Implement a function that tallies how many array elements map to each key produced by an iteratee.

Implement a function that recursively clones a JSON-serializable value without sharing references.

Implement a function that recursively merges two objects, combining nested properties rather than overwriting them.

Implement a function that returns a copy of a value with the given keys stripped from every nested object.

Implement an EventEmitter class supporting on, off, and emit to register and trigger listeners.

Implement an event emitter where subscribe returns a handle whose release method removes that listener.

Implement a function that safely reads a nested object path and returns a default when any segment is missing.

Implement get and set — read and write a nested value by a path like 'a.b[0].c', creating missing containers on set.

Implement a function that buckets array elements into an object keyed by the value an iteratee returns for each.

Implement an instanceof check — walk the prototype chain to see whether a constructor's prototype appears in it.

Implement invert and invertBy — swap an object's keys and values, grouping collisions with invertBy.

Implement a function that decides whether a value is empty across arrays, strings, objects, Maps, Sets, and primitives.

Implement chainable addClass, removeClass, toggleClass, and hasClass helpers on a DOM element wrapper.

Implement a localStorage wrapper that stores values with a TTL and returns null once an entry has expired.

Implement mapKeys and mapValues — transform an object's keys or values while preserving its structure.

Build a simplified in-memory ORM with model delegates that expose basic CRUD operations.

Implement Object.assign — copy own enumerable string and symbol properties from sources onto a target, skipping nullish.

Implement Object.create — make a new object with a given prototype and optional property descriptors.

Implement pick, omit, pickBy, and omitBy — build a subset of an object by a key list or by a predicate.

Implement a function that flattens a nested object into a single-level object using dot-delimited keys.

Implement a minimal test runner that registers cases, runs each one, and reports pass and fail counts.

Build a Turtle class that tracks position and heading as you issue movement and turn commands on a 2D plane.

Implement helpers that accurately identify non-primitive JavaScript values such as arrays, plain objects, dates, and maps.

Implement a function that rebuilds a nested object from a flat map of dot-delimited keys.

Implement a Backbone-style Model class that stores attributes and emits change events per key.

Implement a deep clone that copies nested values and correctly handles circular references using a visited map.

Implement a function that determines whether two values are structurally equal across nested objects and arrays.

Build a simplified in-memory ORM with field selection and eagerly included related records.

Implement structuredClone — deep-clone a value including Map, Set, Date, RegExp, typed arrays, and circular references.

Implement a function that patches shallow style objects over a text range without clobbering unrelated keys.