Why is my list not created in javascript?

I have an object with 4 properties that i want to make to a list using only JS. Could someone help me to see what is wrong with my code? I can't seem to get it to render..

const categoriesOb = {
  animals: ["rabbit", "horse", "dog", "bird"],
  cities: ["malmö", "umeå", "köping", "örebro"],
  fruits: ["banana", "apple", "orange", "pear"],
  movies: ["frost", "jaws", "batman", "avatar"],
};

function makeUl(object) {
  const catList = document.createElement("ul");

  for (let i = 0; i < object.length; i++) {
    const catBtn = document.createElement("li");
    catBtn.className = "catBtn";
    catBtn.appendChild(document.createTextNode(object[i]));
    catList.appendChild(catBtn);
  }
  return catList;
}
document.getElementById("category-container").appendChild(makeUl(categoriesOb));

<div id="category-container"></div>

Object.keys() is what you want here.

Also, using the for...of construct means you won't need to mess around with pointer variables and iterator length.

const categoriesOb = {
  animals: ['rabbit', 'horse', 'dog', 'bird'],
  cities: ['malmö', 'umeå', 'köping', 'örebro'],
  fruits: ['banana', 'apple', 'orange', 'pear'],
  movies: ['frost', 'jaws', 'batman', 'avatar'],
};

function makeUl(object) {
  const catList = document.createElement('ul');

  for (let property of Object.keys(object)) {
    const catBtn = document.createElement('li');
    catBtn.className = 'catBtn';
    catBtn.appendChild(document.createTextNode(property));
    catList.appendChild(catBtn);
  }

  return catList;
}

document.getElementById('category-container').appendChild(makeUl(categoriesOb));

Hope this helps.