Dynamically import module in TypeScript

Question

What is the TypeScript way of loading modules dynamically (path to the module is known at runtime)? I tried this one:

var x = "someplace"
import a = module(x)

But it seems that TypeScript compiler would like to see path as a string in import/module at compile time:

$ tsc test.ts 
/tmp/test.ts(2,19): error TS1003: Identifier expected.
/tmp/test.ts(2,20): error TS1005: ';' expected.

I know I can for example directly use RequireJS (if I use amd module format), but that doesn't feel right to me - it's solution for one particular library.

Answer 1

ES proposal dynamic import is supported since TypeScript 2.4. Document is here.

import function is asynchronous and returns a Promise.

var x = 'someplace';
import(x).then((a) => {
  // `a` is imported and can be used here
});

Or using async/await:

async function run(x) {
  const a = await import(x);
  // `a` is imported and can be used here
}

Answer 2

You need to specify a hard coded string. Variables will not work.

Update

JavaScript now got dynamic imports. So you can do import(x) :https://developers.google.com/web/updates/2017/11/dynamic-import

TypeScript supports it as well. That said you would still want the argument to be statically analyzable for type safety e.g.

const x = 'someplace';
import(x).then((a) => { // TypeScript knows that `x` is 'someplace' and will infer the type of `a` correctly
}); 

Answer 3

If you want to extract the type from a default export dynamically it can be done like so:

    const dynamicImport = await import('path-to-import')
    const typedDefaultImport = dynamicImport.default