Invoking a function defined in JavaScript

Picking up where I left off in the previous post, I am going to cover some ways to get data into a script.

Here’s how to simply supply parameter values when calling a function defined in a script. First the ScriptRunner needs to be updated:

pubic class ScriptRunner {
  ...

  public void load(String scriptName) throws ... {
    Reader reader = resourceReader(scriptName);
    _engine.eval(reader);
  }

  public <T> T invoke(String functionName, Object... params) throws ... {
    //noinspection unchecked
    return (T) ((Invocable) _engine).invokeFunction(functionName, params);
  }

  private InputStreamReader resourceReader(String scriptName) {
    InputStream stream = getClass().getResourceAsStream(scriptName);
    return new InputStreamReader(stream);
  }
}

Now, given some script:

// userdef.js
function expectedSalesTax(productType, unitPrice, quantity) {
  return unitPrice * quantity * 0.0825;   // 8.25%
}

It can be invoked after the script is loaded:

  ScriptRunner runner = new ScriptRunner();
  runner.load("userdef.js");
  double taxes = runner.invoke("expectedSalesTax", "sneakers", 99.90, 5);

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