I decided to update my TypeScript brush plugin for TypeScript 3.0 and also to specify it works with latest WordPress 4.9.8.  The plugin page on WordPress.org is located here – https://wordpress.org/plugins/syntax-highlighter-evolved-typescript/changelog/

Samples (from here and here)

let foo: unknown = 10;

// Since `foo` has type `unknown`, TypeScript
// errors on each of these locations.
foo.x.prop;
foo.y.prop;
foo.z.prop;
foo();
new foo();
upperCase(foo);
foo `hello world!`;

function upperCase(x: string) {
return x.toUpperCase();
}

// TODO (billg): 5 overloads should *probably* be enough for anybody?
function call<T1, T2, T3, T4, R>(fn: (param1: T1, param2: T2, param3: T3, param4: T4) => R, param1: T1, param2: T2, param3: T3, param4: T4): R
function call<T1, T2, T3, R>(fn: (param1: T1, param2: T2, param3: T3) => R, param1: T1, param2: T2, param3: T3): R
function call<T1, T2, R>(fn: (param1: T1, param2: T2) => R, param1: T1, param2: T2): R
function call<T1, R>(fn: (param1: T1) => R, param1: T1): R;
function call<R>(fn: () => R, param1: T1): R;
function call(fn: (...args: any[]) => any, ...args: any[]) {
return fn(...args);
}

export interface Props { name?: string }
export class Greet extends React.Component<Props> {
render() {
const { name } = this.props;

// Notice the `!` ------v
return <div>Hello ${name!.toUpperCase()}!</div>;
}
static defaultProps = { name: "world"}
}

function loudlyGreet(name = "world") {
// Thanks to the default initializer, `name` will always have type `string` internally.
// We don't have to check for `undefined` here.
console.log("HELLO", name.toUpperCase());
}

// Externally, `name` is optional, and we can potentially pass `undefined` or omit it entirely.
loudlyGreet();
loudlyGreet(undefined);

// Some non-TypeScript JSX file

import * as React from "react";
import * as ReactDOM from "react-dom";

export class Greet extends React.Component {
render() {
const { name } = this.props;
return <div>Hello ${name.toUpperCase()}!</div>;
}

static defaultProps = {
name: "world",
};
}

// Notice no `name` attribute was specified!
// vvvvvvvvv
const result = ReactDOM.renderToString(<Greet />);
console.log(result);

import * as _foo from "foo";

export async function bar() {
let foo: typeof _foo = await import("foo");
}

function useKey<T, K extends Extract<keyof T, string>>(obj: T, k: K) {
let propName: string = k;
// ...
}