What is the javascript equivalent of "using"?

Questions & Answers
1

I want to make a custom variable type using Javascript instead of C# if possible. What would be the javascript equivalent of the following lines for my javascript class? (I've done a simple one before in C# to create n dimensional arrays but I'm not familiar enough with C# to do a large complex class with it in a short period of time.)

using UnityEngine;
using System.Collections;

I know javascript files are monobehavior extensions by default but that wouldn't be practical for this class ( A pseudo variable hashtable attached to a file and updating it after any changes ) I'm already using

import System;
import System.IO;

Do I just import System.Collections as well or should that be what it Extends?

2

It's import, yeah, e.g.

import System.Collections.Generic;

For the class itself, don't use an implicit class, use

public class MyClassName
{
    //code
}

That'll let you create your own class however you like, using 

public class MyClassName extends Whatever

to extend other classes