esm.ts

const extensions = {
  js: 'application/javascript',
  ts: 'application/typescript',
  jsx: 'text/jsx',
  tsx: 'text/tsx',
} as const;

type Extensions = typeof extensions;
type ValidExtension = keyof Extensions;
type ValidMediaType = Extensions[ValidExtension];

export default function esm(lang: ValidMediaType) {
  return (text: TemplateStringsArray, ...rest: string[]) => {
    const code = String.raw(text, rest);
    const metadata = `data:${lang};charset=utf-8`;
    const uri = `${metadata},${encodeURIComponent(code)}`;
    return import(uri);
  };
}

export const js = esm(extensions.js);
export const ts = esm(extensions.ts);
export const jsx = esm(extensions.jsx);
export const tsx = esm(extensions.tsx);

export function isValidExtension(ext: string): ext is ValidExtension {
  return ext in extensions;
}

usage.ts

import ts from "./esm.ts"

const module = await ts`export const a = "hi!"`;

console.log(module.a) // hi!

usage2.ts

import * as esm from "./esm.ts"

const path = 'path/to/myfile.ts'
const ext = getExtensionFrom(path)

if (!esm.isValidExtension(ext)) {
  throw new Error(`Invalid extension ${ext}`)
}

const content = await Deno.readTextFile(path)
const module = esm[ext]`${content}`;

// ...