Add examples for built-in types (#35)

2026-02-01 15:59:43 +00:00 · 2019-09-14 06:52:11 +02:00 · 2019-09-14 06:52:11 +02:00 · 108c03bc0a
commit 108c03bc0a
parent d3e30b6e14
1 changed files with 478 additions and 0 deletions
--- a/readme.md
+++ b/readme.md
@ -93,17 +93,495 @@ Click the type names for complete docs.
 There are many advanced types most users don't know about.

 - [`Partial<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1401-L1406) - Make all properties in `T` optional.
+    <details>
+    <summary>
+        Example
+    </summary>
+
+    [Playground](https://typescript-play.js.org/?target=6#code/KYOwrgtgBAMg9gcxsAbsANlA3gKClAeQDMiAaPKAEWACMwFz8BRAJxbhcagDEBDAF17ocAXxw4AliH7AWRXgGNgUAHJwAJsADCcEEQkJsFXgAcTK3hGAAuKAGd+LKQgDcFEx363wEGrLf46IjIaOi28EioGG5iOArovHZ2qhrAAIJmAEJgEuiaLEb4Jk4oAsoKuvoIYCwCErq2apo6egZQALyF+FCm5pY2UABETelmg1xFnrYAzAAM8xNQQZGh4cFR6AB0xEQUIm4UFa0IABRHVbYACrws-BJCADwjLVUAfACUXfhEHFBnug4oABrYAATygcCIhBoACtgAp+JsQaC7P9ju9Prhut0joCwCZ1GUAGpCMDKTrnAwAbWRPWSyMhKWalQMAF0Dtj8BIoSd8YSZCT0GSOu1OmAQJp9CBgOpPkc7uBgBzOfwABYSOybSnVWp3XQ0sF04FgxnPFkIVkdKB84mkpUUfCxbEsYD8GogKBqjUBKBiWIAen9UGut3u6CeqReBlePXQQQA7skwMl+HAoMU4CgJJoISB0ODeOmbvwIVC1cAcIGmdpzVApDI5IpgJscNL49WMiZsrl8id3lrzScsD0zBYrLZBgAVOCUOCdwa+95uIA)
+
+    ```typescript
+    interface NodeConfig {
+        appName: string;
+        port: number;
+    }
+
+    class NodeAppBuilder {
+        private configuration: NodeConfig = {
+            appName: 'NodeApp',
+            port: 3000,
+        };
+
+        config(config: Partial<NodeConfig>) {
+            type NodeConfigKey = keyof NodeConfig;
+
+            for (const key of Object.keys(config) as NodeConfigKey[]) {
+                const updateValue = config[key];
+
+                if (updateValue === undefined)
+                    continue;
+
+                this.configuration[key] = updateValue;
+            }
+
+            return this;
+        }
+    }
+
+    // Partial<NodeConfig> allows us to provide only a part of the
+    // NodeConfig interface.
+    new NodeAppBuilder()
+        .config({ appName: 'ToDoApp' });
+    ```
+    </details>
+
 - [`Required<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1408-L1413) - Make all properties in `T` required.
+    <details>
+    <summary>
+        Example
+    </summary>
+
+    [Playground](https://typescript-play.js.org/?target=6#code/AQ4SwOwFwUwJwGYEMDGNgGED21VQGJZwC2wA3gFCjXAzFJgA2A-AFzADOUckA5gNxUaIYjA4ckvGG07c+g6gF8KQkAgCuEFFDA5O6gEbEwUbLm2ESwABQIixACJIoSdgCUYAR3Vg4MACYAPGYuFvYAfACU5Ko0APRxwADKMBD+wFAAFuh2Vv7OSBlYGdmc8ABu8LHKsRyGxqY4oQT21pTCIHQMjOwA5DAAHgACxAAOjDAAdChYxL0ANLHUouKSMH0AEmAAhJhY6ozpAJ77GTCMjMCiV0ToSAb7UJPPC9WRgrEJwAAqR6MwSRQPFGUFocDgRHYxnEfGAowh-zgUCOwF6KwkUl6tXqJhCeEsxDaS1AXSYfUGI3GUxmc0WSneQA)
+
+    ```typescript
+    interface ContactForm {
+        email?: string;
+        message?: string;
+    }
+
+    function submitContactForm (formData: Required<ContactForm>) {
+        // Send the form data to the server
+    }
+
+    submitContactForm({
+        email: 'ex@mple.com',
+        message: 'Hi! Could you tell me more about...',
+    });
+
+    // TypeScript error: missing property 'message'
+    submitContactForm({
+        email: 'ex@mple.com',
+    });
+    ```
+    </details>
+
 - [`Readonly<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1415-L1420) - Make all properties in `T` readonly.
+    <details>
+    <summary>
+        Example
+    </summary>
+
+    [Playground](https://typescript-play.js.org/?target=6#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)
+
+    ```typescript
+    enum LogLevel {
+        Off,
+        Debug,
+        Error,
+        Fatal,
+    };
+
+    interface LoggerConfig {
+        name: string;
+        level: LogLevel;
+    }
+
+    class Logger {
+        config: Readonly<LoggerConfig>;
+
+        constructor({ name, level }: LoggerConfig) {
+            this.config = { name, level };
+            Object.freeze(this.config);
+        }
+    }
+
+    const config: LoggerConfig = { name: 'MyApp', level: LogLevel.Debug };
+    const logger = new Logger(config);
+
+    // TypeScript Error: cannot assign to read-only property.
+    logger.config.level = LogLevel.Error;
+
+    // We are able to edit config variable as we please.
+    config.level = LogLevel.Error;
+    ```
+    </details>
+
 - [`Pick<T, K>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1422-L1427) - From `T`, pick a set of properties whose keys are in the union `K`.
+    <details>
+    <summary>
+        Example
+    </summary>
+
+    [Playground](https://typescript-play.js.org/?target=6#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)
+
+    ```typescript
+   interface Article {
+        title: string;
+        thumbnail: string;
+        content: string;
+    }
+
+    // Creates new type out of Article interface composed from Articles' two
+    // properties: 'title' and 'thumbnail'.
+    // ArticlePreview = { title: string; thumbnail: string; }
+    type ArticlePreview = Pick<Article, 'title' | 'thumbnail'>;
+
+    // Render a list of articles using only title and description.
+    function renderArticlePreviews(previews: ArticlePreview[]): HTMLElement {
+        const articles = document.createElement('div');
+        for (const preview of previews) {
+            // append preview to the articles
+        }
+        return articles;
+    }
+
+    const articles = renderArticlePreviews([
+        { title: 'TypeScript tutorial!', thumbnail: '/assets/ts.jpg', },
+    ]);
+    ```
+    </details>
+
 - [`Record<K, T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1429-L1434) - Construct a type with a set of properties `K` of type `T`.
+    <details>
+    <summary>
+        Example
+    </summary>
+
+    [Playground](https://typescript-play.js.org/?target=6#code/AQ4ejYAUHsGcCWAXBMB2dgwGbAKYC2ADgDYwCeeemCaWArgE7ADGMxAhmuQHQBQoYEnJE8wALKEARnkaxEKdMAC8wAOS0kstGuAAfdQBM8ANzxlRjXQbVaWACwC0JPB0NqA3HwGgIwAJJoWozYHCxixnAsjAhStADmwESMMJYo1Fi4HMCIaPEu+MRklHj8gpqyoeHAAKJFFFTAAN4+giDYCIxwSAByHAR4AFw5SDF5Xm2gJBzdfQPD3WPxE5PAlBxdAPLYNQAelgh4aOHDaPQEMowrIAC+3oJ+AMKMrlrAXFhSAFZ4LEhC9g4-0BmA4JBISXgiCkBQABpILrJ5MhUGhYcATGD6Bk4Hh-jNgABrPDkOBlXyQAAq9ngYmJpOAAHcEOCRjAXqwYODfoo6DhakUSph+Uh7GI4P0xER4Cj0OSQGwMP8tP1hgAlX7swwAHgRl2RvIANALSA08ABtAC6AD4VM1Wm0Kow0MMrYaHYJjGYLLJXZb3at1HYnC43Go-QHQDcvA6-JsmEJXARgCDgMYWAhjIYhDAU+YiMAAFIwex0ZmilMITCGF79TLAGRsAgJYAAZRwSEZGzEABFTOZUrJ5Yn+jwnWgeER6HB7AAKJrADpdXqS4ZqYultTG6azVfqHswPBbtauLY7fayQ7HIbAAAMwBuAEoYw9IBq2Ixs9h2eFMOQYPQObALQKJgggABeYhghCIpikkKRpOQRIknAsZUiIeCttECBEP8NSMCkjDDAARMGziuIYxHwYOjDCMBmDNnAuTxA6irdCOBB1Lh5Dqpqn66tISIykawBnOCtqqC0gbjqc9DgpGkxegOliyfJDrRkAA)
+
+    ```typescript
+        // Positions of employees in our company.
+    type MemberPosition = 'intern' | 'developer' | 'tech-lead';
+
+    // Interface describing properties of a single employee.
+    interface Employee {
+        firstName: string;
+        lastName: string;
+        yearsOfExperience: number;
+    }
+
+    // Create an object that has all possible `MemberPosition` values set as keys.
+    // Those keys will store collection of Emplyees of the same position.
+    const team: Record<MemberPosition, Employee[]> = {
+        intern: [],
+        developer: [],
+        'tech-lead': [],
+    };
+
+    // Our team has decided to help John with his dream of becoming Software Developer.
+    team.intern.push({ firstName: 'John', lastName: 'Doe', yearsOfExperience: 0 });
+
+    // Record forces you to initialize all of the property keys
+    // TypeScript Error: "tech-lead" property is missing
+    const teamEmpty: Record<MemberPosition, null> = {
+        intern: null,
+        developer: null,
+    };
+    ```
+    </details>
+
 - [`Exclude<T, U>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1436-L1439) - Exclude from `T` those types that are assignable to `U`.
+    <details>
+    <summary>
+        Example
+    </summary>
+
+    [Playground](https://typescript-play.js.org/?target=6#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)
+
+    ```typescript
+    interface ServerConfig {
+      port: null | string | number;
+    }
+
+    type RequestHandler = (req: Request, res: Response) => void;
+
+    // Exclude null type from `null | string | number`.
+    // In case when port is equal to null we will use default value.
+    function getPortValue(port: Exclude<ServerConfig['port'], null>): number {
+      if (typeof port === 'string') return parseInt(port, 10);
+      return port;
+    }
+
+    function startServer(handler: RequestHandler, config: ServerConfig): void {
+      const server = require('http').createServer(handler);
+
+      const port = config.port === null ? 3000 : getPortValue(config.port);
+      server.listen(port);
+    }
+    ```
+    </details>
+
 - [`Extract<T, U>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1441-L1444) - Extract from `T` those types that are assignable to `U`.
+    <details>
+    <summary>
+        Example
+    </summary>
+
+    [Playground](https://typescript-play.js.org/?target=6#code/CYUwxgNghgTiAEAzArgOzAFwJYHtXzSwEdkQBJYACgEoAueVZAWwCMQYBuAKDDwGcM8MgBF4AXngBlAJ6scESgHIRi6ty5ZUGdoihgEABXZ888AN5d48ANoiAuvUat23K6ihMQ9ATE0BzV3goPy8GZjZOLgBfLi4Aejj4AEEICBwAdz54MAALKFQQ+BxEeAAHY1NgKAwoIKy0grr4DByEUpgccpgMaXgAaxBerCzi+B9-ZulygDouFHRsU1z8kKMYE1RhaqgAHkt4AHkWACt4EAAPbVRgLLWNgBp9gGlBs8uQa6yAUUuYPQwdgNpKM7nh7mMML4CgA+R5WABqUAgpDeVxuhxO1he0jsXGh8EoOBO9COx3BQPo2PBADckaR6IjkSA6PBqTgsMBzPsicdrEC7OJWXSQNwYvFEgAVTS9JLXODpeDpKBZFg4GCoWa8VACIJykAKiQWKy2YQOAioYikCg0OEMDyhRSy4DyxS24KhAAMjyi6gS8AAwjh5OD0iBFHAkJoEOksC1mnkMJq8gUQKDNttKPlnfrwYp3J5XfBHXqoKpfYkAOI4ansTxaeDADmoRSCCBYAbxhC6TDx6rwYHIRX5bScjA4bLJwoDmDwDkfbA9JMrVMVdM1TN69LgkTgwgkchUahqIA)
+
+    ```typescript
+    declare function uniqueId(): number;
+    const ID = Symbol('ID');
+
+    interface Person {
+      [ID]: number;
+      name: string;
+      age: number;
+    }
+
+    // Allows change of person data as long as the property key is of string type.
+    function changePersonData<
+      Obj extends Person,
+      Key extends Extract<keyof Person, string>,
+      Value extends Obj[Key]
+    > (obj: Obj, key: Key, value: Value): void {
+      obj[key] = value;
+    }
+
+    // Tiny Andrew was born.
+    const andrew = {
+      [ID]: uniqueId(),
+      name: 'Andrew',
+      age: 0,
+    };
+
+    // Cool, we're fine with that.
+    changePersonData(andrew, 'name', 'Andrea');
+
+    // Goverment didn't like the fact that you wanted to change your identity.
+    changePersonData(andrew, ID, uniqueId());
+    ```
+    </details>
+
 - [`NonNullable<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1446-L1449) - Exclude `null` and `undefined` from `T`.
+    <details>
+    <summary>
+        Example
+    </summary>
+    Works with <code>strictNullChecks</code> set to <code>true</code>. (Read more <a href="https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-0.html">here</a>)
+
+    [Playground](https://typescript-play.js.org/?target=6#code/C4TwDgpgBACg9gJ2AOQK4FsBGEFQLxQDOwCAlgHYDmUAPlORtrnQwDasDcAUFwPQBU-WAEMkUOADMowqAGNWwwoSgATCBIqlgpOOSjAAFsOBRSy1IQgr9cKJlSlW1mZYQA3HFH68u8xcoBlHA8EACEHJ08Aby4oKDBUTFZSWXjEFEYcAEIALihkXTR2YSSIAB54JDQsHAA+blj4xOTUsHSACkMzPKD3HHDHNQQAGjSkPMqMmoQASh7g-oihqBi4uNIpdraxPAI2VhmVxrX9AzMAOm2ppnwoAA4ABifuE4BfKAhWSyOTuK7CS7pao3AhXF5rV48E4ICDAVAIPT-cGQyG+XTEIgLMJLTx7CAAdygvRCA0iCHaMwarhJOIQjUBSHaACJHk8mYdeLwxtdcVAAOSsh58+lXdr7Dlcq7A3n3J4PEUdADMcspUE53OluAIUGVTx46oAKuAIAFZGQwCYAKIIBCILjUxaDHAMnla+iodjcIA)
+
+    ```typescript
+    type PortNumber = string | number | null;
+
+    /** Part of a class definition that is used to build a server */
+    class ServerBuilder {
+        portNumber!: NonNullable<PortNumber>;
+
+        port(this: ServerBuilder, port: PortNumber): ServerBuilder {
+            if (port == null) {
+                this.portNumber = 8000;
+            } else {
+                this.portNumber = port;
+            }
+
+            return this;
+        }
+    }
+
+    const serverBuilder = new ServerBuilder();
+
+    serverBuilder
+        .port('8000')   // portNumber = '8000'
+        .port(null)     // portNumber =  8000
+        .port(3000);    // portNumber =  3000
+
+    // TypeScript Error
+    serverBuilder.portNumber = null;
+    ```
+    </details>
+
 - [`Parameters<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1451-L1454) - Obtain the parameters of a function type in a tuple.
+    <details>
+    <summary>
+        Example
+    </summary>
+
+    [Playground](https://typescript-play.js.org/?target=6#code/GYVwdgxgLglg9mABAZwBYmMANgUwBQxgAOIUAXIgIZgCeA2gLoCUFAbnDACaIDeAUIkQB6IYgCypSlBxUATrMo1ECsJzgBbLEoipqAc0J7EMKMgDkiHLnU4wp46pwAPHMgB0fAL58+oSLARECEosLAA5ABUYG2QAHgAxJGdpVWREPDdMylk9ZApqemZEAF4APipacrw-CApEgBogkKwAYThwckQwEHUAIxxZJl4BYVEImiIZKF0oZRwiWVdbeygJmThgOYgcGFYcbhqApCJsyhtpWXcR1cnEePBoeDAABVPzgbTixFeFd8uEsClADcIxGiygIFkSEOT3SmTc2VydQeRx+ZxwF2QQ34gkEwDgsnSuFmMBKiAADEDjIhYk1Qm0OlSYABqZnYka4xA1DJZHJYkGc7yCbyeRA+CAIZCzNAYbA4CIAdxg2zJwVCkWirjwMswuEaACYmCCgA)
+
+    ```typescript
+    function shuffle(input: any[]): void {
+      // Mutate array randomly changing its' elements indexes.
+    }
+
+    function callNTimes<Fn extends (...args: any[]) => any> (func: Fn, callCount: number) {
+      // Type that represents type of received function parameters.
+      type FunctionParameters = Parameters<Fn>;
+
+      return function (...args: FunctionParameters) {
+        for (let i = 0; i < callCount; i++) {
+          func(...args);
+        }
+      }
+    }
+
+    const shuffleTwice = callNTimes(shuffle, 2);
+    ```
+    </details>
+
 - [`ConstructorParameters<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1456-L1459) - Obtain the parameters of a constructor function type in a tuple.
+    <details>
+    <summary>
+        Example
+    </summary>
+
+    [Playground](https://typescript-play.js.org/?target=6#code/MYGwhgzhAECCBOAXAlqApgWQPYBM0mgG8AoaaFRENALmgkXmQDsBzAblOmCycTV4D8teo1YdO3JiICuwRFngAKClWENmLAJRFOZRAAtkEAHQq00ALzlklNBzIBfYk+KhIMAJJTEYJsDQAwmDA+mgAPAAq0GgAHnxMODCKTGgA7tCKxllg8CwQtL4AngDaALraFgB80EWa1SRkAA6MAG5gfNAB4FABPDJyCrQR9tDNyG0dwMGhtBhgjWEiGgA00F70vv4RhY3hEZXVVinpc42KmuJkkv3y8Bly8EPaDWTkhiZd7r3e8LK3llwGCMXGQWGhEOsfH5zJlsrl8p0+gw-goAAo5MAAW3BaHgEEilU0tEhmzQ212BJ0ry4SOg+kg+gBBiMximIGA0nAfAQLGk2N4EAAEgzYcYcnkLsRdDTvNEYkYUKwSdCme9WdM0MYwYhFPSIPpJdTkAAzDKxBUaZX+aAAQgsVmkCTQxuYaBw2ng4Ok8CYcotSu8pMur09iG9vuObxZnx6SN+AyUWTF8MN0CcZE4Ywm5jZHK5aB5fP4iCFIqT4oRRTKRLo6lYVNeAHpG50wOzOe1zHr9NLQ+HoABybsD4HOKXXRA1JCoKhBELmI5pNaB6Fz0KKBAodDYPAgSUTmqYsAALx4m5nC6nW9nGq14KtaEUA9gR9PvuNCjQ9BgACNvcwNBtAcLiAA)
+
+    ```typescript
+    class ArticleModel {
+      title: string;
+      content?: string;
+
+      constructor(title: string) {
+        this.title = title;
+      }
+    }
+
+    class InstanceCache<T extends (new (...args: any[]) => any)> {
+      private ClassConstructor: T;
+      private cache: Map<string, InstanceType<T>> = new Map();
+
+      constructor (ctr: T) {
+        this.ClassConstructor = ctr;
+      }
+
+      getInstance (...args: ConstructorParameters<T>): InstanceType<T> {
+        const hash = this.calculateArgumentsHash(...args);
+
+        const existingInstance = this.cache.get(hash);
+        if (existingInstance !== undefined) return existingInstance;
+
+        return new this.ClassConstructor(...args);
+      }
+
+      private calculateArgumentsHash(...args: any[]): string {
+        // Calculate hash
+        return 'hash';
+      }
+    }
+
+    const articleCache = new InstanceCache(ArticleModel);
+    const amazonArticle = articleCache.getInstance('Amazon forests burining!');
+    ```
+    </details>
+
 - [`ReturnType<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1461-L1464) – Obtain the return type of a function type.
+    <details>
+    <summary>
+        Example
+    </summary>
+
+    [Playground](https://typescript-play.js.org/?target=6#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-YhAA+qegAAYLKQLQj3ZsEsdccmnGcLor2Dn8xGedHGpEIBzEzspfsfMHDNAANTQACMVaIljV5GQkRA5DYmIpVKQAgAJARO9le33BDXIyi0YuLW2nJFGLqkOvxFB0YPdBSaLZ0IwNzyPkO8-xkGgsLh8Al427a3hWAhXwwHA8EHT5PmgAB1bAQBAANJ24adKWpft72RaBUTgRBUCAj89HAM8xCTaBjggABRQx0DuHJv25P9dCkWRZVIAAiBjoFImpmjlFBgA0NpsjadByDacgIDAEAIAAQmYpjoGYgAZSBsmGPw6DtZiiFA8CoJguDmAQmoZ2QvtUKQLdoAYmBTwgdEiCAA)
+
+    ```typescript
+    /** Provide every element of iterable `iter` into the `callback` function and store results in an array. */
+    function mapIter<
+        Elem,
+        Func extends (elem: Elem) => any,
+        Ret extends ReturnType<Func>
+    >(iter: Iterable<Elem>, callback: Func): Ret[] {
+        const mapped: Ret[] = [];
+
+        for (const elem of iter) {
+            mapped.push(callback(elem));
+        }
+
+        return mapped;
+    }
+
+    const setObject: Set<string> = new Set();
+    const mapObject: Map<number, string> = new Map();
+
+	mapIter(setObject, (v: string) => v.indexOf('Foo')); // number[]
+
+    mapIter(mapObject, ([key, val]: [number, string]) => {
+        return key % 2 === 0 ? val : 'Odd';
+    }); // string[]
+    ```
+    </details>
+
 - [`InstanceType<T>`](https://github.com/Microsoft/TypeScript/blob/2961bc3fc0ea1117d4e53bc8e97fa76119bc33e3/src/lib/es5.d.ts#L1466-L1469) – Obtain the instance type of a constructor function type.
+    <details>
+    <summary>
+        Example
+    </summary>
+
+    [Playground](https://typescript-play.js.org/?target=6#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-YhAA+qegAAYLKQLQj3ZsEsdccmnGcLor2Dn8xGedHGpEIBzEzspfsfMHDNAANTQACMVaIljV5GQkRA5DYmIpVKQAgAJARO9le33BDXIyi0YuLW2nJFGLqkOvxFB0YPdBSaLZ0IwNzyPkO8-xkGgsLh8Al427a3hWAhXwwHA8EHT5PmgAB1bAQBAANJ24adKWpft72RaBUTgRBUCAj89HAM8xCTaBjggABRQx0DuHJv25P9dCkWRZVIAAiBjoFImpmjlFBgA0NpsjadByDacgIDAEAIAAQmYpjoGYgAZSBsmGPw6DtZiiFA8CoJguDmAQmoZ2QvtUKQLdoAYmBTwgdEiCAA)
+
+    ```typescript
+    class IdleService {
+        doNothing (): void {}
+    }
+
+    class News {
+        title: string;
+        content: string;
+
+        constructor(title: string, content: string) {
+            this.title = title;
+            this.content = content;
+        }
+    }
+
+    const instanceCounter: Map<Function, number> = new Map();
+
+    interface Constructor {
+        new(...args: any[]): any;
+    }
+
+    // Keep track how many instances of `Constr` constructor have been created.
+    function getInstance<
+        Constr extends Constructor,
+        Args extends ConstructorParameters<Constr>
+    >(constructor: Constr, ...args: Args): InstanceType<Constr> {
+        let count = instanceCounter.get(constructor) || 0;
+
+        const instance = new constructor(...args);
+
+        instanceCounter.set(constructor, count + 1);
+
+        console.log(`Created ${count + 1} instances of ${Constr.name} class`);
+
+        return instance;
+    }
+
+
+    const idleService = getInstance(IdleService);
+    // Will log: `Created 1 instances of IdleService class`
+    const newsEntry = getInstance(News, 'New ECMAScript proposals!', 'Last month...');
+    // Will log: `Created 1 instances of News class`
+    ```
+    </details>
+
+- [`Omit<T, K>`](https://github.com/microsoft/TypeScript/blob/71af02f7459dc812e85ac31365bfe23daf14b4e4/src/lib/es5.d.ts#L1446) – Constructs a type by picking all properties from T and then removing K.
+    <details>
+    <summary>
+        Example
+    </summary>
+
+    [Playground](https://typescript-play.js.org/?target=6#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-SgfXlHqVUE4xiAA)
+
+    ```typescript
+    interface Animal {
+        imageUrl: string;
+        species: string;
+        images: string[];
+        paragraphs: string[];
+    }
+
+    // Creates new type with all properties of Animal interface except 'images' and
+    // 'paragraphs' properties.
+    // We can use this type to render small hover tooltip for Wiki entry list.
+    type AnimalShortInfo = Omit<Animal, 'images' | 'paragraphs'>;
+
+    function renderAnimalHoverInfo (animals: AnimalShortInfo[]): HTMLElement {
+        const container =  document.createElement('div');
+        // Internal implementation.
+        return container;
+    }
+    ```
+    </details>

 You can find some examples in the [TypeScript docs](https://www.typescriptlang.org/docs/handbook/advanced-types.html#predefined-conditional-types).