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JavaScript source profile

Select the JavaScript source profile with surfaces: ["js"] on a C# or Rust target. The profile supplies JavaScript globals and built-ins; the target supplies their carriers and runtime implementation.

These are native operations, not a JavaScript runtime. See native numbers for integer widths, bitwise operations, numeric predicates and allocation limits.

Covered source families

  • Array and readonly arrays with native dense storage;
  • String, Boolean, Number, and Math;
  • Map, Set, and their iterators;
  • Date;
  • RegExp and the standard string/regular-expression protocols;
  • JSON over closed supported value graphs;
  • Promise, async functions, and selected timer APIs;
  • console;
  • typed arrays and other declarations provided by the active profile.

Each target’s support matrix records implemented operations and precise target limits. See native performance for the native string units, dense-array contract, explicit UTF-16 values and retained ownership costs.

Native strings and JsString

string remains the default source string:

const path: string = "content/index.md";

Exact JavaScript UTF-16 code-unit behavior is explicit:

import { jsstr } from "@tsonic/js/lang.js";
import type { JsString } from "@tsonic/js/types.js";

const value: JsString = jsstr("😀");

Targets must not infer JsString from literals, selected surface, member spelling, or API use. Native APIs such as file-system paths continue to accept ordinary string unless their declared contract says otherwise.

Error stacks

const error = new Error("Cannot load the file");
Error.captureStackTrace(error);
const stack = error.stack;
if (stack !== undefined) console.log(stack);

C# and Rust do not capture stacks during Error construction or when stack is read. Call Error.captureStackTrace(error) explicitly to capture and format the native stack at that call. Aliases and rethrows retain the resulting string; calling it again replaces the previous snapshot. Without capture or an explicit stack assignment, stack is undefined, including for runtime-created errors.

Frame names, filenames, and available debug information belong to the native toolchain. The text is not a V8 stack or a promised mapping to the authored TypeScript. Do not parse it as a portable source-location protocol. Only the explicit call pays capture and formatting costs. Rust requires its std foundation for capture; alloc-only errors still work without stacks. C# retains the CLR’s normal throw-time exception behavior independently of this source stack property. Rust currently supports explicit capture and stack reads, not arbitrary stack-property assignment.

Target references