Attention, pitfall

I just found a very subtle bug in my quartet validation library code , and I want to share it.

Task

Given a list of strings: VALID_STRINGS.

Create a validation function test(x)that should return trueif xis one of the strings in this array.

Scope: x- any Javascript value

Restrictions: Do not use ES6. (Target - old browser)

Solution # 1: A head-on decision

The simplest solution that could be is to go through all the lines in this array and compare.

const VALID_STRINGS = [/* VALID STRINGS */]
function test1(x) {
  for (let i = 0; i < VALID_STRINGS.length; i++) {
    if (VALID_STRINGS[i] === x) return  true
  }
  return false
}

, , . O( VALID_STRINGS)

, (indexOf, includes, some, reduce ...). , .

№2:

, .

. . .

const VALID_STRINGS = [/* VALID STRINGS */]
const VALID_STRINGS_DICT = {}
for (let i = 0; i < VALID_STRINGS.length; i++) {
  const validString = VALID_STRINGS[i]
  VALID_STRINGS_DICT[validString ] = true
}
function test2(x) {
  return VALID_STRINGS_DICT[x] === true
}

!

! !

, . , — VALID_STRINGS. :

// 
const VALID_STRINGS = ['somestring', 'anotherstring']
//    ,     
const VALID_STRINGS_DICT = { somestring: true, anotherstring: true }

const underwaterRock = ['somestring']

test2(underwaterRock) //  true

underwaterRock — true. , test2(x) x .

VALID_STRINGS_DICT[x]

— x . — . — .

['somestring'].toString() === 'somestring'

№3:

x

const VALID_STRINGS = [/* VALID STRINGS */]
const VALID_STRINGS_DICT = {}
for (let i = 0; i < VALID_STRINGS.length; i++) {
  const validString = VALID_STRINGS[i]
  VALID_STRINGS_DICT[string] = true
}
function test2(x) {
  return typeof x === 'string' && VALID_STRINGS_DICT[x] === true
}

, .

№4: Set

ES6. .

const VALID_STRINGS = [/* VALID STRINGS */]
const validStringsSet = new Set(VALID_STRINGS)

function test4(x) { return validStringsSet.has(x) }

, , .

FAQ:

1. Typescript: , , API. typescript .
   
   Typescript. , unknown any. , javascript.
2. " , , , !"
   
   — )
3. includes ? , , .
4. ES6? , , . №3 , . №4 , . .