Executing scripts

Use Execute for statements and declarations, and Evaluate when the resulting JavaScript value matters.

var engine = new Engine();

engine.Execute("function square(x) { return x * x; }", "math.js");
var value = engine.Evaluate("square(6)", "request.js");

Console.WriteLine(value.AsNumber()); // 36

The optional source name appears in JavaScript stack traces and debugger locations.

Invoke functions

Invoke accepts CLR arguments and converts them. Call accepts values already represented as JsValue.

engine.Execute("function add(a, b) { return a + b; }");

var fromClr = engine.Invoke("add", 2, 3);
var add = engine.GetValue("add");
var fromJsValues = engine.Call(add, 4, 5);

A string passed to Invoke names one global property; it is not JavaScript source or a dotted path. Read a nested function first:

engine.Execute("var api = { add: (a, b) => a + b };");
var add = engine.GetValue(engine.GetValue("api"), "add");
var result = engine.Invoke(add, 1, 2);

Top-level var and function declarations create global-object properties. let, const, and class create global lexical bindings, so retrieve those with Evaluate("name"), not GetValue("name").

Prepare repeated code

Parse once when the same program runs repeatedly:

var prepared = Engine.PrepareScript(
    "input.map(x => x * 2)",
    source: "transform.js",
    strict: true);

var result = engine.SetValue("input", new[] { 1, 2, 3 })
    .Evaluate(in prepared);

A Prepared<Script> is reusable and thread-safe and may be shared across engines. The JsValue result is not: objects belong to the engine and realm that created them. Convert output before crossing that boundary; see Working with values.

Each top-level Execute, Evaluate, Invoke, or Call is a separate run and resets ordinary execution budgets. See Execution constraints when one host operation makes several calls.