How to Parse and Execute JavaScript Code within C#?

How to parse and execute JS in C#

The provided C# code includes a class, ScriptEngine, that serves as a wrapper around the Windows Script Engine's COM components. It facilitates both 32-bit and 64-bit environments and allows you to parse and execute JavaScript code.

The code sample offers various ways to interact with the script engine:

Direct expression evaluation:

Console.WriteLine(ScriptEngine.Eval("jscript", "1+2/3"));

This evaluates the given JavaScript expression and prints the result (1.66666666666667).

Function call, with optional arguments:

using (ScriptEngine engine = new ScriptEngine("jscript"))
{
  ParsedScript parsed = engine.Parse("function MyFunc(x){return 1+2+x}");
  Console.WriteLine(parsed.CallMethod("MyFunc", 3));
}

This defines a JavaScript function, parses it, and calls the function with the argument 3, printing the result (6).

Function call with named items, and optional arguments:

using (ScriptEngine engine = new ScriptEngine("jscript"))
{
    ParsedScript parsed = engine.Parse("function MyFunc(x){return 1+2+x+My.Num}");
    MyItem item = new MyItem();
    item.Num = 4;
    engine.SetNamedItem("My", item);
    Console.WriteLine(parsed.CallMethod("MyFunc", 3));
}

[ComVisible(true)] // Script engines are COM components.
public class MyItem
{
    public int Num { get; set; }
}

This example demonstrates the use of named items, which enables emulating/implementing HTML DOM elements. It sets a named item "My" with a property "Num" set to 4, and calls the function with the argument 3, printing the result (10).

The sample also shows how to use a CLSID instead of a script language name to take advantage of the fast IE9 "chakra" JavaScript engine:

using (ScriptEngine engine = new ScriptEngine("{16d51579-a30b-4c8b-a276-0ff4dc41e755}"))
{
    // continue with chakra now
}

The full source code for the ScriptEngine class and sample uses are provided for reference. It includes additional features like:

• Property retrieval and setting
• Script exception handling
• Adding named root-level items to the script engine's name space

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