数组去重

let myArray = ['a', 'b', 'a', 'b', 'c', 'e', 'e', 'c', 'd', 'd', 'd', 'd']
let myArrayWithNoDuplicates = myArray.reduce( (previousValue, currentValue) => {
    if (previousValue.indexOf(currentValue) === -1) {
    previousValue.push(currentValue)
    }
    return previousValue
}, [])
console.log(myArrayWithNoDuplicates)
//output：[ 'a', 'b', 'c', 'e', 'd' ]

arrayWithNoDuplicates = Array.from(new Set(myArray))
console.log(arrayWithNoDuplicates)
//output：[ 'a', 'b', 'c', 'e', 'd' ]
console.log([...new Set(myArray)])
//output：[ 'a', 'b', 'c', 'e', 'd' ]