function getIndex(arr,num){
var len = arr.length,
st = 0,
end = len-1
while(st<=end){
var mid = Math.floor((st+end)/2)
if(num==arr[mid]){
return mid
}else if(num>arr[mid]){
st = mid+1
}else{
end = mid-1
}
}
return arr;
}
var ary=[1,4,7,8,12,34,67,88,99,100]
console.log(getIndex(ary,12))
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