cli-testing-library/src/get-user-code-frame.ts

Simple and complete CLI testing utilities that encourage good testing practices.

// We try to load node dependencies
import fs from "node:fs";
import pc from "picocolors";
import { codeFrameColumns } from "@babel/code-frame";

const readFileSync = fs.readFileSync;

// frame has the form "at myMethod (location/to/my/file.js:10:2)"
function getCodeFrame(frame: string) {
  const locationStart = frame.indexOf("(") + 1;
  const locationEnd = frame.indexOf(")");
  const frameLocation = frame.slice(locationStart, locationEnd);

  const frameLocationElements = frameLocation.split(":");
  const [filename, line, column] = [
    frameLocationElements[0]!,
    parseInt(frameLocationElements[1]!, 10),
    parseInt(frameLocationElements[2]!, 10),
  ];

  let rawFileContents = "";
  try {
    rawFileContents = readFileSync(filename, "utf-8");
  } catch (e) {
    return "";
  }

  const codeFrame = codeFrameColumns(
    rawFileContents,
    {
      start: { line, column },
    },
    {
      highlightCode: false,
      linesBelow: 0,
    },
  );
  return `${pc.dim(frameLocation)}\n${codeFrame}\n`;
}

function getUserCodeFrame() {
  // If we couldn't load dependencies, we can't generate the user trace
  /* istanbul ignore next */
  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
  if (!readFileSync || !codeFrameColumns) {
    return "";
  }
  const err = new Error();
  const firstClientCodeFrame = err.stack
    ?.split("\n")
    .slice(1) // Remove first line which has the form "Error: TypeError"
    .find((frame) => !frame.includes("node_modules/")); // Ignore frames from 3rd party libraries

  return getCodeFrame(firstClientCodeFrame!);
}

export { getUserCodeFrame };