storables

Svelte's built-in stores are not always ergonomic when you have to mix them with imperative code. Storables remedy this by letting you to embed logic within a store's lifetime.

checkable

checkable works like Svelte's writable but with built-in asynchronous validation.

Features

• ✅ Asynchronous validation

  const initialValue = "John Smith";
  const { username, usernameCheckStatus } = checkable({
      name: "username",
      async check(newUsername) {
          // This value is invalid, but I know what I'm doing.
          if (userIsTyping) return false;
          // This value is invalid, scream!
          if (await alreadyExists(newUsername)) {
              throw Error("Username already taken");
          }
          // This value is valid
          return true;
      },
  }, initialValue);

  $usernameCheckStatus is "pending" while validating the value asynchronously.

  $usernameCheckStatus is "done" when validation is complete.

  $usernameCheckStatus is "error" if the validation throws an error.

  In the above example, usernameCheckStatus.error is Error("Username is already taken") if $usernameCheckStatus === "error". It is null otherwise.

  Unlike the transformable's assert, check is not write-blocking.

  The default/initial value is not validated.

persistable

Persist your store's value in localStorage or your database —store it anywhere.

Features

• 💾 Asynchronous storage

  const defaultValue = 0;
  const { count } = persistable({
      name: "count",
      io: {
          read: async () => await readFromDatabase(),
          update(set) {
              const cleanUp = onDatabaseChange((value) => set(value));
              return cleanUp;
          },
          write: async (value) => await writeToDatabase(value),
      },
  }, defaultValue);

• ✅ Validation

  const defaultValue = 0;
  const { count, countWriteStatus } = persistable({
      name: "count",
      io: {
          read: () => JSON.parse(localStorage.getItem("count")),
          write: (value) => {
              if (isInvalid(value)) {
                  throw Error("Could not write invalid value");
              }
              localStorage.setItem("count", JSON.stringify(value));
          },
      },
  }, defaultValue);

  $countWriteStatus is "pending" while writing value.

  $countWriteStatus is "done" when writing is complete.

  $countWriteStatus is "error" if the write throws an error.

  In the above example, countWriteStatus.error is Error("Could not write invalid value") if $countWriteStatus === "error". It is null otherwise.

transformable

If Svelte's built-in writable and derived stores had a baby, it would be transformable.

Features

• 🔄 Two-way transforms (...more like many-way transforms)

  const { dateObject, number } = transformable({
      name: "number",
      transforms: {
          dateObject: {
              to: (date) => date.getTime(),
              from: (number) => new Date(number),
          },
      },
  }, new Date().getTime());

  Updating number will call its own subscribers with $number and subscribers of dateObject with new Date($number). Updating dateObject will call its own subscribers with $dateObject and subscribers of number with $dateObject.getTime().

  This is handy if, for example, you want to display minutes to a user but your code thinks in milliseconds.

• ✅ Validation

  const now = new Date().getTime()
  const { number, numberAssertStatus } = transformable({
      name: "number",
      assert(number) {
          // This is an invalid value, but I know what I'm doing.
          if (number === undefined) return false;
          // This is an error, scream!
          if (number < now) throw Error("Date must be after now");
          // This is a valid number
          return true;
      }
  }, now);

  numberAssertStatus.error is Error("Date must be after now") if $numberAssertStatus === "error". It is null otherwise.

  assert is write-blocking. If it throws or returns false the value of the store will not change and subscribers will not be called.

  The default/initial value is not validated.