What condition can I develop to avoid duplicating values?

Question

How to avoid duplicate numbers in this random generator?

var soma = 0
while (soma < 1000) {
    soma += parseInt(Math.random() * 100)
    document.write(soma + "<br>")
}

As it goes running, it arrives at a certain moment that it brings with it incidences of values.

Answer 1

You can use this code:

var soma = 0;
var numeros = [];
console.log('Soma: ' + soma);
while (soma < 1000) {
   numero = Math.random() * 100;
   if (numeros.indexOf(numero) < 0) {
       numeros.push(numero);
       soma += parseInt(numero);
       console.log('Soma: ' + soma);
   }
}

Answer 2

Suggestion:

Within the while generates a number and checks if it already exists within the array that stores the drawn numbers.

If it exists does continue to the while continue, if it does not exist, add it to the array and add it to the soma.

var soma = 0;
var sorteados = [];
while (soma < 1000) {
  var nr = parseInt(Math.random() * 100, 10) + 1; // +1 para não aceitar "zero"
  if (sorteados.indexOf(nr) > -1) continue;
  soma += nr;
  sorteados.push(nr);
  console.log('Soma:', soma, 'Sorteado:', nr);
}

Answer 3

Works using indexOf as shown, but it would be more efficient (in terms of memory usage) to use a Hashtable, thus:

var soma = 0;
var sorteados = {};
while (soma < 1000) {
   var num = parseInt(Math.random() * 100);
   if (!sorteados.hasOwnProperty(num)) {
     sorteados[num] = true;
     soma += num;
     console.log(soma);
   }
}

Note: It is not recommended to use the function document.write because this rewrites all your DOM, instead you should use javascript to retrieve elements from your DOM and add values or other elements to it.