LevelDB Feature Support Manifest

Common errors

• TypeError: (0, level_supports_1.default) is not a function

  cause Attempting to use `level-supports` v3.0.0 or higher with a default import/require syntax, but the package changed to a named export.
  fix Change your import statement from `import supports from 'level-supports'` to `import { supports } from 'level-supports'` or for CommonJS, `const supports = require('level-supports')` to `const { supports } = require('level-supports')`.

• Error: Persistent storage is required

  cause A consumer of the database is checking for `db.supports.permanence` but the provided manifest or underlying database driver indicates `permanence: false`.
  fix Ensure that the `level-supports` manifest accurately reflects the underlying database's capabilities, especially for critical features like `permanence`. If persistence is required, use a database that provides it or configure the manifest accordingly.

Warnings

• breaking Version 6.0.0 dropped support for Node.js versions older than 16. Ensure your environment meets this requirement.
  Fix: Upgrade your Node.js environment to version 16 or newer. If you need to support older Node.js versions, pin 'level-supports' to '~5.x'.
• breaking Version 5.0.0 removed properties that were implicitly true since 'abstract-level@1'. This streamlines the manifest, focusing on explicit feature declarations.
  Fix: Review your manifest creation and usage. If you were relying on implicit truths for older properties, you might need to explicitly define them if still required, though most were redundant with `abstract-level@1`.
• breaking Version 3.0.0 introduced significant breaking changes: it is no longer compatible with `abstract-leveldown` or `levelup` directly, and it changed from a default export to a named export (`{ supports }`). Additionally, `encodings` and `events` properties are now always objects.
  Fix: Update import statements from `const supports = require('level-supports')` to `const { supports } = require('level-supports')` or `import { supports } from 'level-supports'`. Ensure your database implementations are `abstract-level` compatible. Adjust manifest property checks for `encodings` and `events` to expect objects.
• gotcha Manifest properties are truthy rather than strictly boolean. When checking for support, always use `if (db.supports.feature)` instead of `if (db.supports.feature === true)` to accommodate future extensibility where features might have object values.
  Fix: Adopt the `if (db.supports.feature)` pattern for all feature checks to ensure forward compatibility.
• deprecated `implicitSnapshots` is aliased as `snapshots` for backwards compatibility. While `snapshots` still works, `implicitSnapshots` is the preferred and more descriptive property name.
  Fix: Update code referencing `db.supports.snapshots` to `db.supports.implicitSnapshots` for clarity and future-proofing.

Install

• npm install level-supports npm
• yarn add level-supports yarn
• pnpm add level-supports pnpm

Imports

• supports
  wrong:

  const supports = require('level-supports')

  correct:

  import { supports } from 'level-supports'

  Since v3.0.0, 'level-supports' exports a named 'supports' function, not a default export. CommonJS 'require' still works, but ESM import is preferred in modern Node.js environments.
• supports

  const { supports } = require('level-supports')

  This is the correct CommonJS pattern for named exports. Prior to v3.0.0, it was a default export accessed as `const supports = require('level-supports')`.
• Manifest

  import type { Manifest } from 'level-supports'

  TypeScript type for the manifest object is available for better type safety when defining custom manifests or consuming the generated one.

Quickstart

Demonstrates how to create a support manifest, attach it to a database object, and check for specific features like permanence, encodings, and `has()`.

import { supports } from 'level-supports';

// Simulate a database with specific capabilities
const myCustomDb = {
  // In a real scenario, these would come from the database driver
  supports: supports({
    permanence: true,
    encodings: {
      utf8: true,
      json: { value: true, array: false },
      binary: {} // Truthy, details allowed
    },
    implicitSnapshots: true,
    explicitSnapshots: false,
    has: true
  })
};

console.log(`Database supports permanence: ${!!myCustomDb.supports.permanence}`);
console.log(`Database supports JSON encoding: ${!!myCustomDb.supports.encodings.json}`);

if (myCustomDb.supports.has) {
  console.log('Database implements has() and hasMany().');
} else {
  console.log('Database does not implement has().');
}

// Merge with another manifest (e.g., from a plugin)
const pluginManifest = { signals: true };
const mergedSupports = supports(myCustomDb.supports, pluginManifest);
console.log(`Database supports signals (after merge): ${!!mergedSupports.signals}`);