The method used to re-array flattening method +

Deduplication Array:

var arr = [
1,1,'true','true',true,true,15,15,false,false, 
undefined,undefined, null,null, NaN, NaN,'NaN', 0, 0, 'a',
'a',{a:1,b:2},{a:1,b:2}
];

//1
function unique(arr){
    var obj = {}
    return arr.filter(function(item, index, arr){
        return obj.hasOwnProperty(typeof item + item) ?
             false : (obj[type item + item] = true)
    })
}

//2
arr1 = [... new Set(arr)]
//3
arr2 = Array.from(new Set(arr))
//4
let obj = {}
arr.forEach(item => {
    obj[item] = 1
})
Object.keys(obj).map(o => Number(o))

Flat array:

//1
function flatten(arr){
    return arr.toString().split(',').map(item => {
        return Number(item)
    })
}
//2
function flatten(arr){
    return arr.join(',').split(',').map(item => {
        return parseInt(item)
    })
}
//3
arr1 = arr.flat(Infinity)
//4
function flatten(item){
    return items.reduce((prev, current) => {
        return prev.concat(Array.isArray(current) ? 
            flatten(current) : current
        )
    }, [])
}