Find missing number code in which contagious in array.

var a=[1,2,3,4,5,6,8,10]
function getMissingNo(arr, N) {
let bag=""
for(var i=0;i<arr.length;i++){
for(var j=i+1;j<arr.length;j++){
if(arr[i]+1==arr[j]){
// console.log(arr[i],"yes",arr[j])
i++
}else{
bag+=arr[i]+1+","
i++
}
}

}
console.log(bag)
}
console.log(getMissingNo(a,a.length))