1. var arr=[1,1,1,3,3,7,7,4,7,3];
    2. var a=[];
    3. var b=[];
    4. for(let i=0;i < arr.length;i++){
    5.     if(a[arr[i]] == undefined){
    6.         a[arr[i]] = true;
    7.         b.push(arr[i]);
    8.     }
    9. }
    10. console.log(b);//[ 1, 3, 7, 4 ]