localStorage without the footguns

localStorage stores strings only, is synchronous, and throws in private mode or when full. Wrap reads in try/catch and never touch it during server rendering.

#storage#browser#json

javascript

function readJSON(key, fallback) {
  try {
    const raw = localStorage.getItem(key);
    return raw ? JSON.parse(raw) : fallback;
  } catch {
    return fallback;
  }
}

function writeJSON(key, value) {
  try {
    localStorage.setItem(key, JSON.stringify(value));
  } catch {
    /* quota exceeded or blocked */
  }
}

Array methods you reach for

`map` transforms, `filter` narrows, `reduce` folds. All three return new values — none of them mutate. `sort` and `reverse` DO mutate, so copy first with `toSorted` or a spread.

localStorage without the footguns

Related

Array methods you reach for