NTE supports fully customizable control of rendering and other features using JavaScript code. This page lists the various functions, objects, etc. provided when using JavaScript in NTE.

The main purpose of this feature is to implement dynamic displays on trains, but you have to keep in mind that the interface of the displays, the logic of operation, and so on, varies greatly from city to city and from train to train around the world.

If a simple format was chosen, it would not be possible to flexibly reproduce the actual interface, and there would be a lot of requests and complaints; if a more complex format was developed to implement the logic, the result would be something like JS, but not as easy to learn and use as JS. So in the end it was decided to use the JS runtime to maximize flexibility.

Any text editor will do, such as Notepad3 or Notepad++. You may want to use something like Visual Studio Code. Using IDEA/Visual Studio will probably be unnecessary.

This article assumes that you have some basic understanding of JavaScript, so it won't delve into the basic syntax and other aspects of JavaScript here, you can learn JavaScript from resources on the web, such as here. Reminder: JavaScript has nothing to do with Java.

As you know, values ​​in JS have different types. When calling a function, you must pass parameters of the appropriate type, and the result it returns will also have a type. In this article, the parameter and return types of the provided functions are denoted in a form similar to TypeScript. For example:

• static Resources.id(idStr: String): ResourceLocation

  • static means that you don't need to create an object to use this function, you can call Resources.id(“aaa:bbb”) directly.
  • idStr: String means that the idStr parameter accepts a string.
  • : ResourceLocation means that a function call will return a value of type ResourceLocation.

• Matrices.rotateX(radian: float): void

  • The lack of static means that an object is required to execute the function. For example, if a is an object of Matrices type, then the function can be called as a.rotateX(Math.PI).
  • radian: float means that the parameter takes a numeric argument. Although JS does not distinguish between integers and fractional numbers, this article will specify a specific type - int, long, float or double - to make it clear whether a parameter can accept decimal parts and to what precision.
  • : void means that the function has no return value.
  • : ResourceLocation means that a function call will return a value of type ResourceLocation.

The Rhino JS engine allows using classes from the standard Java library as java.package.name. Using classes from MTR is not available yet, most likely due to problems with the class loader.

NTE uses JavaScript's strict mode, which does not allow variables to be assigned immediately without declaring them. To declare a global variable, use syntax like var glb; or outside a function var glb = 1;. To use local variables inside a function, use let local; or let local = 1;.

[Translator's note: in general, it is better to always try to use let and resort to using var as a last resort].

NTE calls the function you wrote once per frame and expects your function to finish processing and return a value as soon as possible. Therefore, there is no such thing as “stop execution and wait for a while”. If you want to achieve this behavior, you need to time it and then execute the appropriate action on a call made at the right time.

If locks or infinite loops occur in the code, the entire script execution will stall because NTE scripts are executed one at a time [in the same thread]. This can be reset with F3+T.

For common function types such as strings, Java and JavaScript have different class implementations, which causes there to be JavaScript strings as well as Java strings. NTE/MTR functions and fields return Java string classes rather than JavaScript strings, but Rhino does some conversions automatically, so in most cases you can mix and match, but sometimes this can cause problems.

For example, here's an example of a problem caused by using str.length() from a Java string class and str.length from a JavaScript string class to get the length of a string:

var stationName = train.getThisRoutePlatforms().get(0).station.name;
print(stationName.length); // Error: stationName is a Java string, not a JavaScript string
print(stationName.length()); // Java strings get their length from the length() function, not the JavaScript length field
print((""+stationName).length) // Use ""+ to turn it into a JavaScript string.

Similarly, there is a List<T> type in Java. It does the same thing as arrays in JavaScript, but has a different type. Trying to call JavaScript array functions on it won't work, but Rhino adapts it so that you can take values with list[0] or loop through them with for (a of list).

The Rhino engine does not support all of the latest JavaScript features. See Mozilla's documentation for details on what is supported. NTE uses Rhino 1.7.14 with the VERSION_ES6 flag enabled.

If the script is executed incorrectly, NTE will report an error in the Minecraft log (starting with “Error in NTE Resource Pack JavaScript”), but there will be no in-game message. The error message will indicate which line of code in which script file the error occurred. Most launchers have the ability to display logs in a separate window in real time.

In addition, NTE pauses the script for 4 seconds and then tries to run it again.

• static include(relPath: String): void

  • Loads and runs another JS file relative to the current JS file.

• static include(path: ResourceLocation): void

  • Loads and runs the JS file by location in the resource pack. For example, include(Resources.id(“mtr:path/absolute.js”)).