React

by ronnjoe

HTML

<div id="app"></div>

CSS

body {
  background: #20262E;
  padding: 20px;
  font-family: Helvetica;
}

#app {
  background: #fff;
  border-radius: 4px;
  padding: 20px;
  transition: all 0.2s;
}

li {
  margin: 8px 0;
}

h2 {
  font-weight: bold;
  margin-bottom: 15px;
}

.done {
  color: rgba(0, 0, 0, 0.3);
  text-decoration: line-through;
}

input {
  margin-right: 5px;
}

React

const items = [{
  id: 1,
  category: "cat_1",
  title: "My title 1"
}, {
  id: 2,
  category: "cat_2",
  title: "My title 2"
}, {
  id: 6,
  category: "cat_1",
  title: "Another title 1"
}, {
  id: 1,
  category: "cat_3",
  title: "My title 3"
}, {
  id: 8,
  category: "cat_1",
  title: "Third Title"
}, {
  id: 2,
  category: "cat_2",
  title: "Another title 2 "
}];
const cats = items.reduce((catsSoFar, { category, title }) => {
  if (!catsSoFar[category]) catsSoFar[category] = [];
  catsSoFar[category].push(title);
  return catsSoFar;
}, {});
console.log(cats);