git init

.gitignore

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+node_modules/
+build/
+.idea/

package.json

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+{
+  "name": "activitypub-js-models",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "type": "module",
+  "scripts": {
+    "ts:watch": "tsc -p ./tsconfig.json",
+    "start": "node --es-module-specifier-resolution=node build/index.js",
+    "start:dev": "nodemon --es-module-specifier-resolution=node build/index.js"
+  },
+  "author": "",
+  "license": "ISC",
+  "devDependencies": {
+    "nodemon": "^2.0.20",
+    "typescript": "^4.8.4"
+  }
+}

src/index.ts

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+import express from 'express';
+import { ObjectAP } from './models/Object.model';
+
+// const app = express();
+// app.listen(3000, () => console.log('Listening on port 3000!'));
+
+const obj = new ObjectAP({
+    id: 'someId',
+});
+const obj2 = new ObjectAP({
+    cc: '123',
+    content: obj,
+}).addContext();
+
+console.log(obj2.plain());
+console.log(obj2.json());

src/models/Activity.model.ts

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+import {ModelBaseAP} from "./Base.model";
+import {IntransitiveActivityAPFields} from "./IntransitiveActivity.model";
+
+// TODO: types
+// https://www.w3.org/TR/activitystreams-core/#activities
+export interface ActivityAPFields extends IntransitiveActivityAPFields {
+    object?: any; // Object?
+}
+
+export class ActivityAP extends ModelBaseAP<ActivityAPFields>{
+    constructor(fields: ActivityAPFields) {
+        super(fields);
+    }
+}

src/models/Actor.model.ts

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+import {ModelBaseAP} from "./Base.model";
+import {ObjectAPFields} from "./Object.model";
+
+export enum ActorTypes {
+    Application = 'Application',
+    Group = 'Group',
+    Organization = 'Organization',
+    Person = 'Person',
+    Service = 'Service'
+}
+
+// TODO: types
+// https://www.w3.org/TR/activitystreams-core/#actors
+export interface ActorAPFields extends ObjectAPFields {
+    type?: any | ActorTypes; // ?
+    actor?: any; // Actor?
+    target?: any;
+    origin?: any;
+    result?: any;
+    instrument?: any;
+}
+
+export class ActorAP extends ModelBaseAP<ActorAPFields>{
+    constructor(fields: ActorAPFields) {
+        super(fields);
+    }
+}

src/models/Base.model.ts

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+// TODO: types
+export type Context = string | any[];
+
+export interface ModelBaseAPWithContext {
+    '@context'?: Context;
+}
+
+export class ModelBaseAP<T> {
+    public fields: T & ModelBaseAPWithContext;
+
+    constructor(fields: T) {
+        // TODO: make recursive copy
+        this.fields = {
+            ...fields,
+        } as T & ModelBaseAPWithContext;
+    }
+
+    // TODO: rewrite (better option to handle multiple contexts)
+    public addContext(context?: Context): this {
+        this.fields = {
+            ['@context']: context || 'https://www.w3.org/ns/activitystreams',
+            ...this.fields
+        }
+        return this;
+    }
+
+    public plain(): Record<string, any> {
+        const result = {} as Record<string, any>;
+        for (const [key, node] of Object.entries(this.fields)) {
+            if (node instanceof ModelBaseAP) {
+                result[key] = node.plain();
+            } else {
+                result[key] = node;
+            }
+        }
+        // TODO make recursive copy
+        return result;
+    }
+
+    public json() {
+        return JSON.stringify(this.plain());
+    }
+}

src/models/IntransitiveActivity.model.ts

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+import {ModelBaseAP} from "./Base.model";
+import {ObjectAPFields} from "./Object.model";
+
+// TODO: types
+// https://www.w3.org/TR/activitystreams-core/#intransitiveactivities
+export interface IntransitiveActivityAPFields extends ObjectAPFields {
+    actor?: any; // Actor?
+    target?: any;
+    origin?: any;
+    result?: any;
+    instrument?: any;
+}
+
+export class IntransitiveActivityAP extends ModelBaseAP<IntransitiveActivityAPFields>{
+    constructor(fields: IntransitiveActivityAPFields) {
+        super(fields);
+    }
+}

src/models/Link.model.ts

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+import {ModelBaseAP} from "./Base.model";
+
+// TODO: types
+// https://www.w3.org/TR/activitystreams-core/#dfn-link
+export interface ObjectAPFields {
+    id?: any;
+    name?: any;
+    hreflang?: any;
+    mediaType?: any;
+    rel?: any;
+    height?: any;
+    width?: any;
+}
+
+export class LinkAP extends ModelBaseAP<ObjectAPFields>{
+    constructor(fields: ObjectAPFields) {
+        super(fields);
+    }
+}

src/models/Object.model.ts

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+import {ModelBaseAP} from "./Base.model";
+
+// TODO: types
+// https://www.w3.org/TR/activitystreams-core/#object
+export interface ObjectAPFields {
+    id?: any;
+    type?: any;
+    attachment?: any;
+    attributedTo?: any;
+    audience?: any;
+    content?: any;
+    name?: any;
+    endTime?: any;
+    generator?: any;
+    icon?: any;
+    image?: any; // Link?
+    inReplyTo?: any;
+    location?: any;
+    preview?: any;
+    published?: any;
+    replies?: any;
+    startTime?: any;
+    summary?: any;
+    tag?: any;
+    updated?: any;
+    url?: any;
+    to?: any;
+    bto?: any;
+    cc?: any;
+    bcc?: any;
+    mediaType?: any;
+    duration?: any;
+}
+
+export class ObjectAP extends ModelBaseAP<ObjectAPFields>{
+    constructor(fields: ObjectAPFields) {
+        super(fields);
+    }
+}

tsconfig.json

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+{
+  "compilerOptions": {
+    "watch": true,
+    "outDir": "./build",
+    "target": "es2016",
+    "module": "ES6",
+    "moduleResolution": "Node",
+    "esModuleInterop": true,
+    "forceConsistentCasingInFileNames": true,
+    "strict": true,
+    "skipLibCheck": true
+  },
+  "include": ["src/**/*"],
+  "exclude": ["node_modules", "**/*.spec.ts"],
+}