Barebone example of how typescript instruments your source code

typewiz-instrument.ts

import * as fs from 'fs';
import * as ts from 'typescript';

class Replacement {
  public static insert(pos: number, text: string) {
      return new Replacement(pos, pos, text);
  }

  constructor(readonly start: number, readonly end: number, readonly text = '') {}
}

export function applyReplacements(source: string, replacements: Replacement[]) {
  replacements = replacements.sort((r1, r2) => r2.start - r1.start);
  for (const replacement of replacements) {
      source = source.slice(0, replacement.start) + replacement.text + source.slice(replacement.end);
  }
  return source;
}

function visit(node: ts.Node, replacements: Replacement[], fileName: string) {
  if (ts.isFunctionDeclaration(node)) {
    for (const param of node.parameters) {
      const params = [
        JSON.stringify(param.name.getText()),
        param.name.getText(),
        param.name.getEnd(),
        JSON.stringify(fileName),
      ];
      const instrumentExpr = `console.log(${params.join(',')});\n`;
      replacements.push(
        Replacement.insert(node.body.getStart() + 1, instrumentExpr),
      );
    }
  }
  node.forEachChild((child) => visit(child, replacements, fileName));
}

function instrument(fileName: string, sourceCode: string) {
  const sourceFile = ts.createSourceFile(fileName, sourceCode, ts.ScriptTarget.Latest, true);
  const replacements: Replacement[] = [];
  visit(sourceFile, replacements, inputFile);
  console.log(applyReplacements(sourceCode, replacements));
}

const inputFile = process.argv[2];
instrument(inputFile, fs.readFileSync(inputFile, 'utf-8'));