random-weight.js

function rand(min, max) {
  return Math.floor(Math.random() * max) + min
}

function getRandomValue(list, weight) {
  var totalWeight = weight.reduce((p, c) => p + c, 0);
  var randomRatio = rand(0, totalWeight);
  
  for (var i = 0; i < list.length; i++) {
    if (randomRatio < weight[i]) {
      return list[i];
    }
    
    randomRatio = randomRatio - weight[i];
  }
  
  return false;
}

setInterval(() => {
  console.log(getRandomValue(['js', 'php', 'ruby'], [90, 5, 5]));
}, 1000);