69. implement deep equal `_.isEqual()`

JavaScriptLodash
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_.isEqual is useful when you want to compare complex data types by value not the reference.

Can you implement your own version of deep equal isEqual? The lodash version covers a lot of data types. In this problem, you are asked to support :

  1. primitives
  2. plain objects (object literals)
  3. array

Objects are compared by their own, not inherited, enumerable properties

const a = {a: 'bfe'}
const b = {a: 'bfe'}

isEqual(a, b) // true
a === b // false

const c = [1, a, '4']
const d = [1, b, '4']

isEqual(c, d) // true
c === d // false

Lodash implementation has some strange behaviors. (github issue, like following code


const a = {}
a.self = a
const b = {self: a}
const c = {}
c.self = c
const d = {self: {self: a}}
const e = {self: {self: b}}

lodash.isEqual gives us following result. Notice there is a case that resulting in false.

// result from lodash implementation
_.isEqual(a, b) // true
_.isEqual(a, c) // true
_.isEqual(a, d) // true
_.isEqual(a, e) // true
_.isEqual(b, c) // true
_.isEqual(b, d) // true
_.isEqual(b, e) // false
_.isEqual(c, d) // true
_.isEqual(c, e) // true
_.isEqual(d, e) // true

Setting aside the performance concerns mentioned by lodash, your implement should not have above problem, which means above all returns true and call stack should not exceed the maximum.

Let's try to solve this problem within 10 mintues.

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