JCM:Scripting:Documentation
Scripting Documentation
JCM Scripting is a feature introduced in JCM v2.0.0-beta.5. It serves as a testbed for scripting in MTR 4, as well as using JavaScript to control PIDS.
The system itself is heavily influenced by the Nemo Transit Expansion and shares much of the similarities. As such, most of the documentation include this page is also referenced from the NTE JS documentation.
Currently the only supported type of scripting is PIDS Scripting, check Scripted PIDS Documentation for more detail.
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Introduction
How To Edit JavaScript Files?
A JavaScript file (.js) can be edited in a variety of editors. It is recommended to have a text editor that supports JavaScript Syntax Highlighting like Notepad++ or Sublime text. While a full IDE (like Visual Studio Code or IntelliJ) is not recommended, it can also be used as a basic text editor.
This rest of this article assumes that you have a basic understanding of JavaScript and JavaScript types, so it won't delve into the basic syntax and other aspects of it here. You can learn JavaScript from resources on the web, such as here.
Type Annotation
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, all of the functions have their parameter and return types stated. For example:
static Resources.id(idStr: string): Identifier
staticmeans that you don't need to create an object to use this function, you can callResources.id("aaa:bbb")directly.idStr: stringmeans that theidStrparameter accepts a string.: Identifiermeans that a function call will return a value of typeIdentifier.
Matrices.rotateX(radian: float): void
- The lack of
staticmeans that an object is required to execute the function. For example, ifais an object of Matrices type, then the function can be called asa.rotateX(Math.PI). radian: floatmeans 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,floatordouble- to make it clear whether a parameter can accept decimal parts and to what precision.: voidmeans that the function has no return value.
Using Built-In Java Classes
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.
Declaring variables using let or var
Both NTE and JCM 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].
Don't Block Or Infinitely Loop
JCM 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 JCM scripts are executed one by one at a time [in the same thread]. This can be reset with F3+T.
Differences In Using Java Classes
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).
Supported Parts Of The JavaScript Standard
The Rhino engine does not support all of the latest JavaScript features. See Mozilla's documentation for details on what is supported. JCM uses Rhino 1.7.15 with the VERSION_ES6 flag enabled.
Errors
If the script is executed incorrectly, JCM will report an error in the Minecraft log(Starting with “[JCM] [Scripting] Error executing script!”), but please note that there will be no in-game indication. 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.
JCM will then pause the entire script for 4 seconds before executing the function again.
Running Other Scripts
| Functions | Description |
|---|---|
static include(relPath: String): void
|
Loads and runs another JS file relative to the current JS file. |
static include(path: Identifier): void
|
Loads and runs the JS file by location in the resource pack.
For example, |