Detailed discussion of several methods for deduplicating JavaScript arrays

 function funSet(arr){
   return Array.from(new Set(arr));
 }

function funFor(arr){
  for(let i=0,len=arr.length;i<len;i++){
    for(let j=i+1,len=arr.length;j<len;j++){
      if (arr[i]===arr[j]){
        arr.splice(j,1);
        len--;
        j--;
      }
    }
  }
  return arr;
}

function funIndex(arr){
  let newArr = [];
  for(let i=0;i<arr.length;i++){
    if (newArr.indexOf(arr[i])===-1){
      newArr.push(arr[i])
    }
  }
  return newArr;
}

function funInclude(arr){
  let newArr = [];
  for(let i=0;i<arr.length;i++){
    if (!newArr.includes(arr[i])){
      newArr.push(arr[i])
    }
  }
  return newArr;
}

function funFilter(arr){
  return arr.filter(function(item,index){
    return arr.indexOf(item,0)===index;
  })
}

function funMap(arr){
  let map = new Map();
  let newArr = [];
  for(let i=0,len=arr.length;i<len;i++){
    if (map.has(arr[i])){
      map.set(arr[i],true);
    }else{
      map.set(arr[i],false);
      newArr.push(arr[i]);
    }
  }
  return newArr;
}