Arrays - Find missing numbers in a Sequence

ES6-Style

var arr = [0189459, 0189460, 0189461, 0189463, 0189465]; 
var [min,max] = [Math.min(...arr), Math.max(...arr)];
var out = Array.from(Array(max-min),(v,i)=>i+min).filter(i=>!arr.includes(i));

Result: [189462, 189464]

Watch your leading zeroes, they will be dropped when the array is interpreted-

var A= [0189459, 0189460, 0189461, 0189463, 0189465]

(A returns [189459,189460,189461,189463,189465])

function absent(arr){
    var mia= [], min= Math.min.apply('',arr), max= Math.max.apply('',arr);
    while(min<max){
        if(arr.indexOf(++min)== -1) mia.push(min);
    }
    return mia;
}

var A= [0189459, 0189460, 0189461, 0189463, 0189465]; alert(absent(A))

/* returned value: (Array) 189462,189464 */

If you know that the numbers are sorted and increasing:

for(var i = 1; i < numArray.length; i++) {
    if(numArray[i] - numArray[i-1] != 1) {
           //Not consecutive sequence, here you can break or do whatever you want
    }
}

To find a missing number in a sequence, First of all, We need to sort an array. Then we can identify what number is missing. I am providing here full code with some test scenarios. this code will identify only missing positive number, if you pass negative values even then it gives positive number.

function findMissingNumber(inputAr) {
  // Sort array
  sortArray(inputAr);

  // finding missing number here
  var result = 0;
  if (inputAr[0] > 1 || inputAr[inputAr.length - 1] < 1) {
    result = 1;
  } else {
    for (var i = 0; i < inputAr.length; i++) {
      if ((inputAr[i + 1] - inputAr[i]) > 1) {
        result = inputAr[i] + 1;
      }
    }
  }
  if (!result) {
    result = inputAr[inputAr.length - 1] + 1;
  }
  return result;
}

function sortArray(inputAr) {
  var temp;
  for (var i = 0; i < inputAr.length; i++) {
    for (var j = i + 1; j < inputAr.length; j++) {
      if (inputAr[j] < inputAr[i]) {
        temp = inputAr[j];
        inputAr[j] = inputAr[i];
        inputAr[i] = temp;
      }
    }
  }
}

console.log(findMissingNumber([1, 3, 6, 4, 1, 2]));
console.log(findMissingNumber([1, 2, 3]));
console.log(findMissingNumber([85]));
console.log(findMissingNumber([86, 85]));
console.log(findMissingNumber([0, 1000]));