How to structure utility class

Alternative way:

1. Export constants in your utils.ts file:

   export const doSomething = (val: string): any => {
     return val;
   };
   
   export const doSomethingElse = (val: string): any => {
     return val;
   };
   

2. Import and use this methods in main *.ts file:

   import { doSomething, doSomethingElse } from './util';
   ...
   let value1 = doSomething('abc');
   let value2 = doSomethingElse ('efg');
   

There's a couple problems here:

1. You're not instantiating anything, and doSomething is an instance method
2. When you do import * as util, util represents the module, not an object in it.

If you want Util, you should just import that:

import { Util } from './util'

Next, you should instantiate Util, before finally calling the method on it:

var u = new Util();
u.doSomething("test");

Here's your code patched up:

import { Util } from './util'

export class MyClass{
     constructor()
     {
         var u = new Util();
         u.doSomething("test");
     }
}

---

All that said, there seems to be something odd about the way you're using your utils. This is totally personal opinion, but I wouldn't invoke methods that "do something", i.e. cause side effects, in a constructor.

Also, the methods in Util don't really look like they need to be in that class, since the class holds no state that they depend on. You can always export regular functions from a module. If you wrote your utils module like this:

export function doSomething(val: string) { return val; }

export function doSomethingElse(val: string) { return val; }

you'd be exporting your functions directly and would sidestep the instantiation hassle, and in fact your original code would work correctly as is.

If you create a file utils.ts which contains

export default class Utils {
    static doSomething(val: string) { return val; }
    static doSomethingElse(val: string) { return val; }
}

then you can simplify your client code like this:

import Utils from './utils'

export class MyClass {
     constructor()
     {
         Utils.doSomething("test");
     }
}