Proof of Work · Challenge

Implement deep equality

Decide if two values are the same thing, all the way down.

about 25 min · 7 required tests · in the browser

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BriefThe task, the rules and the examples

Memoization, change detection, and assertion libraries all need to answer one question: are these two values the same, even if they are not the same object? === only says yes for the same reference.

Implement deepEqual(a, b). It returns true when the two values have the same structure and contents.

It must handle:

Primitives, compared strictly. 1 and "1" are different. null and undefined are different.
NaN, which equals NaN here even though NaN === NaN is false.
Arrays, compared item by item, in order. Different lengths are different.
Plain objects, compared by keys and values. Key order does not matter. Nested values are compared the same way.
Date objects, equal when they hold the same time.

Two values with different sets of keys are never equal, in either direction.

deepEqual({ a: [1, { b: 2 }] }, { a: [1, { b: 2 }] }) // true
deepEqual({ a: 1, b: 2 }, { b: 2, a: 1 })             // true
deepEqual({ a: 1 }, { a: 1, b: undefined })            // false
deepEqual(new Date(0), new Date(1))                    // false

Maps, Sets, and class instances are out of scope.

Write a top-level function named deepEqual. Do not use export or module.exports.

solution.js

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Graded on

0/7

compares primitives strictlyopen
treats NaN as equal to NaNopen
compares arrays item by item, in orderopen
compares nested objects, ignoring key orderopen
is not fooled by objects with different key setsopen
compares Dates by their time, not as empty objectsopen
does not confuse arrays, objects, and nullopen
BONUS: handles a structure that refers to itselfopen

Other builds

Implement deep equality

Decide if two values are the same thing, all the way down.

about 25 min · 7 required tests · in the browser

deepEqual({ a: [1, { b: 2 }] }, { a: [1, { b: 2 }] }) // true deepEqual({ a: 1, b: 2 }, { b: 2, a: 1 }) // true deepEqual({ a: 1 }, { a: 1, b: undefined }) // false deepEqual(new Date(0), new Date(1)) // false