diff --git a/src/ecs.js b/src/ecs.js
new file mode 100644
index 0000000..03be401
--- /dev/null
+++ b/src/ecs.js
@@ -0,0 +1,124 @@
+import { TreapSet } from "./misc/treap.js";
+
+export class EntityRegistry {
+	constructor() {
+		this.free_ids = new TreapSet();
+		this.signatures = [];
+		this.components = [];
+		this.component_map = new Map();
+	}
+
+	requireComponentList(cname) {
+		if (!this.component_map.has(cname)) {
+			this.component_map.set(cname, this.components.length);
+			this.components.push([]);
+		}
+		return this.components[this.component_map.get(cname)];
+	}
+
+	componentListLowerBound(cl, entity) {
+		if (cl.length === 0) {
+			return 0;
+		} else if (cl[cl.length - 1].__owner_entity < entity) {
+			return cl.length;
+		}
+
+		let l = 0, r = cl.length - 1, p = 0;
+		while (l <= r) {
+			let mid = (l + r) >>> 1;
+			if (cl[mid].__owner_entity < entity) {
+				l = mid + 1;
+			} else {
+				p = mid;
+				r = mid - 1;
+			}
+		}
+		return p;
+	}
+
+	assign(entity, cv) {
+		const cname = cv.constructor.name;
+		const cl = this.requireComponentList(cname);
+
+		cv.__owner_entity = entity;
+		const p = this.componentListLowerBound(cl, entity);
+		
+		if (cl[p]?.__owner_entity === entity) {
+			cl[p] = cv;
+			return this;
+		}
+
+		cl.splice(p, 0, cv);
+		this.signatures[entity][this.component_map.get(cname)] = p;
+		return this;
+	}
+
+	create() {
+		let id = this.free_ids.takeInstance();
+		if (id == null) {
+			id = this.signatures.length;
+		} else {
+			this.free_ids.erase(id);
+		}
+
+		this.signatures[id] = [];
+		return id;
+	}
+
+	destory(entity) {
+		for (let i in this.signatures[entity]) {
+			const p = this.signatures[entity][i];
+			this.components[i].splice(p, 1);
+		}
+
+		this.signatures[entity] = undefined;
+		this.free_ids.insertRaw(entity);
+		return this;
+	}
+
+	getRaw(entity, cid) {
+		return this.components[cid][this.signatures[entity][cid]];
+	}
+
+	get(entity, ctype) {
+		if (!this.component_map.has(ctype.name)) {
+			return null;
+		}
+
+		const cid = this.component_map.get(ctype.name);
+		if (this.signatures[entity][cid] == null) {
+			return null;
+		}
+		return this.getRaw(entity, cid);
+	}
+
+	forEach(rc, func) {
+		if (rc.length === 0) {
+			for (let i = 0; i < this.signatures.length; ++i) {
+				if (this.signatures[i]) {
+					func.call(this, i);
+				}
+			}
+			return this;
+		}
+
+		const rcid = rc.map(ctype => this.component_map.get(ctype.name));
+
+		let p, v = Infinity;
+		for (let cid of rcid) {
+			const cl = this.components[cid];
+			if (cl.length < v) {
+				v = cl.length;
+				p = cid;
+			}
+		}
+
+		for (let c of this.components[p]) {
+			const e = c.__owner_entity;
+			if (rcid.every(cid => this.signatures[e][cid] != null)) {
+				func.apply(this, [e].concat(rcid.map(cid => this.getRaw(e, cid))));
+			}
+		}
+		return this;
+	}
+};
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diff --git a/tests/ecs.test.js b/tests/ecs.test.js
new file mode 100644
index 0000000..0df5cbe
--- /dev/null
+++ b/tests/ecs.test.js
@@ -0,0 +1,59 @@
+import assert from 'node:assert';
+import { EntityRegistry } from '../src/ecs.js';
+
+class Position {
+	constructor(x, y) {
+		this.x = x;
+		this.y = y;
+	}
+}
+
+describe('ECS', function () {
+	it('create', function () {
+		let registry = new EntityRegistry();
+		let id = registry.create();
+	});
+
+	it('destory', function () {
+		let registry = new EntityRegistry();
+		let id0 = registry.create();
+		let id1 = registry.destory(id0).create();
+		assert.equal(id0, id1);
+	});
+
+	it('component', function () {
+		let registry = new EntityRegistry();
+		let id3;
+		for (let i = 0; i < 5; i += 1) {
+			let e = registry.create();
+			registry.assign(e, new Position(i, i));
+			if (i == 3) {
+				id3 = e;
+			}
+		}
+		assert.equal(registry.get(id3, Position).x, 3);
+	});
+
+	it('forEach', function () {
+		let registry = new EntityRegistry();
+		let id3;
+		registry.create();
+		registry.create();
+		for (let i = 0; i < 5; i += 1) {
+			let e = registry.create();
+			registry.assign(e, new Position(i, i));
+			if (i == 3) {
+				id3 = e;
+			}
+		}
+		let count = 0;
+		registry.forEach([], () => {
+			count += 1;
+		});
+		assert.equal(count, 7);
+		registry.forEach([Position], (id, pos) => {
+			pos.x += 1;
+		});
+		assert.equal(registry.get(id3, Position).x, 4);
+	});
+});
\ No newline at end of file