Add multiple descriptors with numeric keys

different-obj-descriptors-with-cache.js

function createDescriptor(key) {
  return {
    enumerable: true,
    get() {
      // do some stuff
      return this.data[key];
    },
    set(value) {
      // do some stuff
      this.data[key] = value;
    }
  };
}

function getDescriptors(from, amount) {
  const descriptors = getDescriptors.cache.slice(from, amount);
  const missing = amount - descriptors.length;
  
  if (missing > 0) {
    const newDescriptors = Array
      .apply(null, {length: missing})
      .map((undef, index) => createDescriptor(from + index));

    getDescriptors.cache.push(...newDescriptors);

    descriptors.push(...newDescriptors);
  }
  
  return descriptors;
}

getDescriptors.cache = [];

function addProperties(arrayLikeObj, from, amount) {
  const descriptorsToAdd = Array(from).concat(getDescriptors(from, amount));

  Object.defineProperties(arrayLikeObj, descriptorsToAdd);
}

same-object-descriptor.js

var obj = {};
var from = 30;
var amount = 40;
var propDesc = {
    configurable: false,
    writable: true,
    enumerable: true,
    value: 300
};
var allPropDescs = Array(from + amount + 1).fill(propDesc, from);
Object.defineProperties(obj, allPropDescs);