typescript module as function

Here's one way to consider breaking it up, and have code-completion/intellisense work. There are a few options that would be closer to the original JavaScript implementation, however, getting code-completion to work can be a bit challenging.

The primary function _ is exported, and returns an exported class called Chained. It's in this class, where the functions that hang from the return value of _ would exist.

In the implementation file (sample.ts):

export class Chained {
    constructor(private val: number) {
    } 
    seconds(): number {
        return this.val / 1000;
    }
}

export function _(val: number): Chained {
    return new Chained(val);
}

And then in use:

/// <reference path="sample.ts" />

import sample = require('./sample');
// create a simple alias for the exported _ function:
import _ = sample._;

var val = _(5000).seconds();
console.log(val);

The output would be 5 as seconds divides the original number by 1000.

If you needed the function to be available like:

_.seconds

as well as:

_().seconds()

Your options become more limited as while TypeScript supports extending a Function instance with properties, intellisense doesn't work:

// this won't work well:
export function _(val:number) : Chained {
   return new Chained(val);
}

_["seconds"] = (val:number) : number => {
   return val / 1000;
}