JavaScripts

#1: Set does not allow duplicate

const num =[1,2,2,3]
console.log(num)                                 // [1,2,2,3]
console.log(num.length)                       //4

console.log(new Set(num))                   // {1,2,3}
console.log([...new Set(num)])                // [1,,2,3]

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#2 seal
#3 fredeze