Datahike JavaScript API

January 17, 2026 · View on GitHub

Status: Beta - API is functional and tested, but may receive breaking changes. Published as datahike@next on npm.

Overview

The Datahike JavaScript API provides a Promise-based interface for Node.js and browser environments. All async operations return Promises, and data is automatically converted between JavaScript and ClojureScript.

Project Structure

src/datahike/js/
  ├── api.cljs          # Main JS API implementation
  ├── api_macros.clj    # Macro for generating API functions
  ├── naming.cljc       # Shared naming conventions (ClojureScript → JavaScript)
  └── typescript.clj    # TypeScript definition generator

npm-package/
  ├── test.js                # Comprehensive test suite
  ├── package.template.json  # Version-controlled template
  ├── README.md             # npm package documentation
  ├── PUBLISHING.md         # Publishing guide
  └── index.d.ts            # Generated TypeScript definitions

bb/src/tools/
  └── npm.clj              # Build automation (version, types, compile, test)

Build Configuration

The JS API uses a modern automated build pipeline:

# Full build: version + types + compile + test
bb npm-build

# Individual steps:
bb npm-version    # Generate package.json from template with version from config.edn
bb codegen-ts     # Generate TypeScript definitions
bb npm-test       # Run npm package tests

Versions are automatically calculated as major.minor.commit-count from config.edn.

Output is generated in npm-package/datahike.js.api.js with advanced compilation.

Installation

npm install datahike@next

Usage

Basic Example

const d = require('datahike');
const crypto = require('crypto');

async function example() {
  // Configuration - must use UUID for :id
  const config = {
    store: {
      backend: ':memory',
      id: crypto.randomUUID()
    }
  };

  // Create database
  await d.createDatabase(config);

  // Connect
  const conn = await d.connect(config);

  // Define schema
  // Keys: WITHOUT colon (plain strings)
  // Values: WITH colon prefix (keywords)
  const schema = [
    {
      'db/ident': ':name',
      'db/valueType': ':db.type/string',
      'db/cardinality': ':db.cardinality/one'
    },
    {
      'db/ident': ':age',
      'db/valueType': ':db.type/long',
      'db/cardinality': ':db.cardinality/one'
    }
  ];
  await d.transact(conn, schema);

  // Insert data (data keys without colons)
  const data = [
    { name: 'Alice', age: 30 },
    { name: 'Bob', age: 25 }
  ];
  await d.transact(conn, data);

  // Get database value (synchronous)
  const db = await d.db(conn);

  // Get datoms
  const datoms = await d.datoms(db, ':eavt');
  console.log('Datoms:', datoms.length);

  // Pull API (pattern attributes with colons)
  const entityId = 1; // Find ID through query or datoms
  const pulled = await d.pull(db, [':name', ':age'], entityId);
  console.log('Entity:', pulled);

  // Clean up
  d.release(conn);
  await d.deleteDatabase(config);
}

Data Conversion

Datahike uses universal EDN conversion rules that are consistent across Python, JavaScript, and Java bindings:

Keys are always keywordized. Values starting with : become keywords, everything else remains literal.

JavaScript → ClojureScript

  • Object keys: Always converted to keywords (: prefix added automatically)
  • String values starting with :: Converted to keywords (e.g., ":memory" → :memory)
  • String values starting with \\:: Literal colon string (e.g., "\\:literal" → ":literal")
  • Other string values: Remain as strings
  • Arrays: Converted to CLJ vectors
  • Numbers, booleans, null: Pass through unchanged
  • UUID strings: Auto-detected and converted to UUID objects (convenience feature)

ClojureScript → JavaScript

  • Keywords: Converted to strings with : prefix
  • CLJ maps: Converted to JS objects (keyword keys become strings)
  • Vectors/Lists: Converted to Arrays
  • Sets: Converted to Arrays
  • Special: DB values, datoms, and connections pass through unchanged

For complete conversion rules and edge cases, see EDN Conversion Documentation.

Important Notes

Keyword Syntax

The universal EDN conversion rules make keyword syntax simple and predictable:

Simple rule: Keys never need :, values that should be keywords need :

// ✅ Schema definition
const schema = [{
  'db/ident': ':name',              // Key auto-keywordized, value is keyword
  'db/valueType': ':db.type/string', // Both become keywords
  'db/cardinality': ':db.cardinality/one'
}];

// ✅ Data insertion
const data = [
  { name: 'Alice', age: 30 }        // Keys auto-keywordized, values are literals
];

// ✅ Configuration
const config = {
  store: {
    backend: ':memory',                // ":memory" becomes :memory keyword
    id: 'test'                      // "test" stays as string
  },
  'schema-flexibility': ':read',    // ":read" becomes :read keyword
  'keep-history?': true             // boolean passes through
};

// ✅ Pull patterns (array of keyword strings)
const pattern = [':name', ':age'];   // Strings with : become keywords

// ✅ Literal colon strings (rare)
const data = [{
  description: '\\:starts-with-colon'  // Escaped → ":starts-with-colon" (string)
}];

Backend Configuration

const crypto = require('crypto');

// In-memory backend (requires UUID)
const memConfig = {
  store: {
    backend: ':memory',
    id: crypto.randomUUID()
  }
};

// File backend (Node.js only)
const fileConfig = {
  store: {
    backend: ':file',
    path: '/path/to/db'
  }
};

Async Operations

All database operations return Promises. Use await or .then():

// Using await (recommended)
const conn = await d.connect(config);
const result = await d.transact(conn, data);
console.log(result['tx-data']);      // Note: 'tx-data' not 'tx_data'
console.log(result['db-before']);
console.log(result['db-after']);

// Using promises
d.connect(config).then(conn => {
  return d.transact(conn, data);
}).then(result => {
  console.log(result['tx-data']);
});

API Functions

All functions use camelCase naming. The JavaScript API automatically:

  • Converts kebab-case → camelCase
  • Removes ! and ? suffixes
  • Renames with → withDb (reserved keyword)

Main API Functions:

  • Database Lifecycle: createDatabase, deleteDatabase, databaseExists
  • Connection: connect, release
  • Database Values: db, asOf, since, history, withDb, dbWith
  • Transactions: transact (async, returns Promise), loadEntities
  • Queries: q, pull, pullMany, datoms, seekDatoms, entity, entityDb
  • Schema: schema, reverseSchema
  • Utilities: tempid, isFiltered, filter, indexRange
  • Maintenance: gcStorage
  • Info: datahikeVersion

Note: transact! from Clojure becomes transact in JavaScript (the ! is removed).

TypeScript Support

Full TypeScript definitions are automatically generated and included:

import * as d from 'datahike';

interface Config {
  store: {
    backend: string;
    id?: string;
    path?: string;
  };
  'keep-history'?: boolean;
  'schema-flexibility'?: string;
}

const config: Config = {
  store: { backend: ':memory', id: 'example' }
};

async function example() {
  await d.createDatabase(config);
  const conn = await d.connect(config);
  const db = d.db(conn);
  // TypeScript will check types automatically
}

Testing

The comprehensive test suite in npm-package/test.js covers all functionality:

  • Basic database operations
  • Schema and transactions
  • Datoms API
  • Pull API
  • Entity API
  • Temporal databases (history, as-of, since)
  • File backend persistence
  • Query API

Run tests with:

bb npm-test

Tests are automatically run in CI/CD as part of bb check.

Naming Conventions

Naming is centralized in src/datahike/js/naming.cljc for consistency:

;; Functions to skip (incompatible with JS or aliases)
(def js-skip-list #{'transact})  ; sync version, use transact! instead

;; Conversion rules:
;; database-exists? → databaseExists
;; create-database  → createDatabase
;; transact!        → transact (! removed)
;; with             → withDb (reserved keyword)

Adding New Functions

  1. Add to API specification: Function must be in datahike.api.specification
  2. Update skip list (if needed): Add to js-skip-list in naming.cljc to exclude
  3. Rebuild package: 
    bb npm-build
    This will:
    • Generate TypeScript definitions (using naming.cljc)
    • Compile API functions (using api_macros.clj)
    • Run tests

Version Management

Versions are calculated automatically from config.edn:

  • Format: major.minor.commit-count
  • Example: 0.6.1637 (major: 0, minor: 6, commits: 1637)
  • package.json is generated from package.template.json during build

Publishing to npm

See npm-package/PUBLISHING.md for detailed publishing instructions.

Quick workflow:

# 1. Build and test
bb npm-build

# 2. Verify package
cd npm-package && npm pack --dry-run

# 3. Publish as next
npm publish --tag next

Known Limitations

Query API

The Datalog query API requires EDN string format:

// ✅ Works: EDN string format
const results = await d.q(
  '[:find ?name ?age :where [?e :name ?name] [?e :age ?age]]',
  db
);

// ❌ Doesn't work: JavaScript object syntax
// const results = await d.q({ find: '?e', where: [...] }, db);

// ✅ Alternative: Use Datoms API for simple queries
const datoms = await d.datoms(db, ':eavt');

Entity API

The entity function returns ClojureScript objects, not plain JavaScript objects. Use the Pull API for plain data:

// ✅ Recommended: Pull API returns plain objects
const data = await d.pull(db, [':name', ':age'], entityId);
console.log(data.name); // Works

// ⚠️ Entity API returns ClojureScript objects
const entity = await d.entity(db, entityId);
// Accessing attributes requires understanding ClojureScript objects

Compilation Warnings

Shadow-cljs compilation may produce warnings from dependencies:

  • BigInt warnings from persistent-sorted-set (harmless, ES2020 feature)
  • Infer warnings (cosmetic, doesn't affect functionality)
  • Redef warning for filter (expected, intentional override)

These can be safely ignored.

Development

Adding New Functions

Functions are automatically generated from datahike.api.specification by the emit-js-api macro. To add a function:

  1. Add it to api-specification in src/datahike/api/specification.cljc
  2. Add to js-skip-list in api_macros.clj if it should be excluded
  3. Rebuild with npx shadow-cljs compile npm-release

Data Conversion Rules

If you need to handle special types, update clj->js-recursive and js->clj-recursive in src/datahike/js/api.cljs.

Current Release

Published as datahike@next on npm. Install with:

npm install datahike@next

Future Improvements

  • Add transaction builder helpers for common patterns
  • Fluent/chainable API for queries
  • Convenience wrappers for common query patterns
  • Improved error messages for JavaScript users
  • Helper module with EDN type constructors (similar to Python's edn.keyword(), kw.DB_ID constants)

See Also